IB Chemistry Resonance, Delocalization of Ozone and Benzene

25
http://lawrencekok.blogs pot.com Prepared by Lawrence Kok Tutorial on Resonance, Delocalization and catalytic destruction of Ozone.

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IB Chemistry Resonance, Delocalization of Ozone and Benzene

Transcript of IB Chemistry Resonance, Delocalization of Ozone and Benzene

Page 1: IB Chemistry Resonance, Delocalization of Ozone and Benzene

httplawrencekokblogspotcom

Prepared by Lawrence Kok

Tutorial on Resonance Delocalization and catalytic destruction of Ozone

Delocalization of electrons

Resonance structures ozone

resonance structure 1 resonance structure 2

resonance hybrid

Ozone3O

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

UV radiation

Ozone at stratosphere

strongest radiation

Delocalization of electrons

Resonance structures ozone

resonance structure 1 resonance structure 2

resonance hybrid

bull All bonds O-O are identical in length and strengthbull Hybrid of 2 resonance structuresbull NO O-O (single) or O=O (double) bonds foundbull Only O ----- O bondbull Intermediate in character bet single and double bond

bull Bond Order = 211

Ozone3O

Click here on video ozone

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

bull Pale blue gas polar dimagneticbull Oxidizing agentbull Potent respiratory hazard and pollutant at ground levelbull Beneficial prevent UV BC from reaching Earth surfacebull Highest ozone level in stratosphere (10 km and 50 km)

UV radiation

Ozone at stratosphere

strongest radiation

3O

FORMAL CHARGE (FC)

Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge

Formula formal charge

V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule

Formal charge sulfur dioxide

formal charge for O

L +

formal charge for Oformal charge for O

L + L + L +

FORMAL CHARGE (FC)

Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge

Formula formal charge

V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule

Formal charge sulfur dioxide

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4

L +

FC = 6 ndash (4 +2) = 0

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2

FC = 6 ndash (6+1) = -1

formal charge for O

V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6

FC = 6 ndash (2+3) = +1

All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion

0+1

-1

L + L + L +

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Click here on ozone depletion substances ODS (phaseout)

Why ozone able to absorb UV B and UV C

Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation

Ozone depletion

UV Exposure

Ozone Hole

Ozone absorb UV radiation

Ozone absorb UV BC

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth How Ozone

protect

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 2: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Delocalization of electrons

Resonance structures ozone

resonance structure 1 resonance structure 2

resonance hybrid

Ozone3O

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

UV radiation

Ozone at stratosphere

strongest radiation

Delocalization of electrons

Resonance structures ozone

resonance structure 1 resonance structure 2

resonance hybrid

bull All bonds O-O are identical in length and strengthbull Hybrid of 2 resonance structuresbull NO O-O (single) or O=O (double) bonds foundbull Only O ----- O bondbull Intermediate in character bet single and double bond

bull Bond Order = 211

Ozone3O

Click here on video ozone

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

bull Pale blue gas polar dimagneticbull Oxidizing agentbull Potent respiratory hazard and pollutant at ground levelbull Beneficial prevent UV BC from reaching Earth surfacebull Highest ozone level in stratosphere (10 km and 50 km)

UV radiation

Ozone at stratosphere

strongest radiation

3O

FORMAL CHARGE (FC)

Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge

Formula formal charge

V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule

Formal charge sulfur dioxide

formal charge for O

L +

formal charge for Oformal charge for O

L + L + L +

FORMAL CHARGE (FC)

Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge

Formula formal charge

V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule

Formal charge sulfur dioxide

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4

L +

FC = 6 ndash (4 +2) = 0

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2

FC = 6 ndash (6+1) = -1

formal charge for O

V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6

FC = 6 ndash (2+3) = +1

All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion

0+1

-1

L + L + L +

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Click here on ozone depletion substances ODS (phaseout)

Why ozone able to absorb UV B and UV C

Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation

Ozone depletion

UV Exposure

Ozone Hole

Ozone absorb UV radiation

Ozone absorb UV BC

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth How Ozone

protect

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 3: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Delocalization of electrons

Resonance structures ozone

resonance structure 1 resonance structure 2

resonance hybrid

bull All bonds O-O are identical in length and strengthbull Hybrid of 2 resonance structuresbull NO O-O (single) or O=O (double) bonds foundbull Only O ----- O bondbull Intermediate in character bet single and double bond

bull Bond Order = 211

Ozone3O

Click here on video ozone

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

bull Pale blue gas polar dimagneticbull Oxidizing agentbull Potent respiratory hazard and pollutant at ground levelbull Beneficial prevent UV BC from reaching Earth surfacebull Highest ozone level in stratosphere (10 km and 50 km)

UV radiation

Ozone at stratosphere

strongest radiation

3O

FORMAL CHARGE (FC)

Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge

Formula formal charge

V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule

Formal charge sulfur dioxide

formal charge for O

L +

formal charge for Oformal charge for O

L + L + L +

FORMAL CHARGE (FC)

Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge

Formula formal charge

V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule

Formal charge sulfur dioxide

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4

L +

FC = 6 ndash (4 +2) = 0

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2

FC = 6 ndash (6+1) = -1

formal charge for O

V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6

FC = 6 ndash (2+3) = +1

All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion

0+1

-1

L + L + L +

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Click here on ozone depletion substances ODS (phaseout)

Why ozone able to absorb UV B and UV C

Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation

Ozone depletion

UV Exposure

Ozone Hole

Ozone absorb UV radiation

Ozone absorb UV BC

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth How Ozone

protect

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 4: IB Chemistry Resonance, Delocalization of Ozone and Benzene

FORMAL CHARGE (FC)

Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge

Formula formal charge

V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule

Formal charge sulfur dioxide

formal charge for O

L +

formal charge for Oformal charge for O

L + L + L +

FORMAL CHARGE (FC)

Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge

Formula formal charge

V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule

Formal charge sulfur dioxide

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4

L +

FC = 6 ndash (4 +2) = 0

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2

FC = 6 ndash (6+1) = -1

formal charge for O

V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6

FC = 6 ndash (2+3) = +1

All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion

0+1

-1

L + L + L +

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Click here on ozone depletion substances ODS (phaseout)

Why ozone able to absorb UV B and UV C

Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation

Ozone depletion

UV Exposure

Ozone Hole

Ozone absorb UV radiation

Ozone absorb UV BC

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth How Ozone

protect

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 5: IB Chemistry Resonance, Delocalization of Ozone and Benzene

FORMAL CHARGE (FC)

Formal ChargebullToolModel for comparing which Lewis structures is more acceptablebullTreats covalent bond with equal electron distribution no electronegativity differences bet atombullElectronegative atom has negative while least electronegative atom has positive formal charge

Formula formal charge

V - valence electrons of atom L ndash lone pair electronB ndash bonding electron molecule

Formal charge sulfur dioxide

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4

L +

FC = 6 ndash (4 +2) = 0

formal charge for O

V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2

FC = 6 ndash (6+1) = -1

formal charge for O

V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6

FC = 6 ndash (2+3) = +1

All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion

0+1

-1

L + L + L +

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Click here on ozone depletion substances ODS (phaseout)

Why ozone able to absorb UV B and UV C

Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation

Ozone depletion

UV Exposure

Ozone Hole

Ozone absorb UV radiation

Ozone absorb UV BC

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth How Ozone

protect

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 6: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Click here on ozone depletion substances ODS (phaseout)

Why ozone able to absorb UV B and UV C

Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation

Ozone depletion

UV Exposure

Ozone Hole

Ozone absorb UV radiation

Ozone absorb UV BC

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth How Ozone

protect

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 7: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Ozone Good and Bad Good Side Bad Side

Ozone in Strastopherebull blocks UV B + C

Ozone in Troposphere act asbull Greenhouse gas

Ozone in ground level act as bullPollutant bullPhotochemical

Click here on ozone depletion substances ODS (phaseout)

Why ozone able to absorb UV B and UV C

Breakdown of ozone ndash High UV radiation ndash Skin cancer - DNA mutation

Ozone depletion

UV Exposure

Ozone Hole

Ozone absorb UV radiation

Ozone absorb UV BC

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth How Ozone

protect

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 8: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Ozone absorb UV radiation

Ozone absorb UV BC

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth How Ozone

protect

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 9: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 10: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Ozone absorb UV radiation

Ozone absorb UV BC

Ozone formation

O=O Double bond

O=O=OInter

mediate

Bond lengthpm 121 127

Bond enthalpykJ mol-1

498 364

Bond order 2 15

Dissociation by UV

lt242nm

lt330nm

Ozone weaker bondbullAbsorb UV AB(wavelength 330nm)

Bonding O2 and O3

Oxygen stronger bondbullAbsorb UV C (wavelength 230nm)

Free radical -reactive species with unpair electron

How ozone layer protect life on earth

Ozone Cycle

How Ozone

protect

Oxygen split by high UV to O (radical)

O radical combine to form ozone

1

2

3 Ozone (stratosphere) absorb UV BC

4Ozone reform again

Ozone cycle

Ozone createddestroyed by Chapman cycle

Oxygen reform again

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 11: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 12: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 13: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Ozone absorb UV BC

CFC breaks down

How CFC breaks down

High UV BC

How CI radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

How CFC destroys ozone

CI free radicals form

CImiddot react O3 form CIOmiddot radical

CIOmiddot react Omiddot form CImiddot radical again

Net eqn- ozone break down

Carbon

Fluorine

Chlorine

CI radical catalyzes again

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 14: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Ozone absorb UV BC

How NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 15: IB Chemistry Resonance, Delocalization of Ozone and Benzene

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 16: IB Chemistry Resonance, Delocalization of Ozone and Benzene

+

Ozone absorb UV BC

NOx breaks down

How CFC breaks down

High UV BCHow NO radical destroy ozone

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

NO free radicals form

NO react O3 form NO2 radical

NO2 react O form NO radical again

Net eqn- ozone breaks down

Oxides of Nitrogen

Nitrogen Dioxide (NO2)

Nitrogen monoxide (nitric oxide NO)

Nitrous oxideN2O

Break down to form NO free radical (unpair electron)

NO NO2

NO2 NO + O2

Sources of NOx

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 17: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 18: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

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Page 19: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Catalytic destruction of ozone

Ozone Depleting Substances (ODS)

Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)

Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane

CFCbullContain chlorine fluorine and carbon atomsbullExtremely stable with strong bonds long half lifebullStability allows CFC into the stratosphere bullHigh UV radiation reacts with CFCbullHigh UV photons breaks CFC (photochemical decomposition) bull Free Cl radicals form - destroying ozone

Trichloroflouromethane CFC-11

Dichlorodifluoromethane CFC-12

Chlorodifluoromethane HCFC-22

Why halogenate

d CFC used

Less harmful

Very harmful

Why fluorinated is safer

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 20: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Kekule

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 21: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Delocalization of electrons

Resonance bull Describing delocalization of electrons within a moleculepolyatomic ion where bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nucleibullπ electrons are sharedbullπ electrons spread ndash more stable

Resonance structures benzene

Benzene6HC6

resonance structure 1 resonance structure 2

Resonance hybrid

bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond

bull Bond Order =

bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center

15

Click here to view

Delocalized electrons

Kekuleacute structure Cyclohexa- 135 triene

χ doublesingle bonds bet them

Benzene

Hexagonal planar

Resonance Hybrid more stable than any of the resonance structure

Click here to view

Kekule

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 22: IB Chemistry Resonance, Delocalization of Ozone and Benzene

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

3 Evidence for Benzene structure1

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 23: IB Chemistry Resonance, Delocalization of Ozone and Benzene

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 24: IB Chemistry Resonance, Delocalization of Ozone and Benzene

ResonanceDelocalization Energy

ΔH cyclohexene = -120kJmol-1

ΔH cyclohexa 13 diene = -240kJmol-1

ΔH cyclohexa 135 triene = -360kJmol-1

ΔH Benzene = -208kJmol-1

Enthalpy change hydrogenation

χ

helliphellip

bull Benzene lower in energy by 150kJbull More stable due to delocalization of π electrons

150kJ-150

C-CSingle bond

C=CDouble bond

C=CBenzene

Bond lengthpm 154 134 140

Bond enthalpykJmol-1

346 614 507

3 Evidence for Benzene structure1

2

Click here evidence against Kekule

bull X ray hit benzene crystalbull Interact with electron (electron density

map) bull X ray diffraction producedbull Bond length measured

X ray crystallography

NO singledouble bond detected

3 Addition reaction for unsaturated C=C

Addition reaction

Substitution reaction

NO double bond

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom

Page 25: IB Chemistry Resonance, Delocalization of Ozone and Benzene

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttpspaceplacenasagovgreenhouseenhttpwwwozonedepletioninfoeducationpart3ozonesourceshtmlhttpcreativecommonsorglicenseshttpwwwciesinorgdocs011-462011-462htmlhttpwwwepmagazineorgstorage165benzene-evidenceaspx

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttplawrencekokblogspotcom