IB Chemistry on Electrophilic Addition and Synthetic routes

Electrophile - Electron deficient - Accept lone pair - Positive charge - Lewis Acid

C - Br

Reactivity for halogenoalkane • Carbon bond to halogen – F, CI, Br, I • High electronegativity on halogen gp • High reactivity – due to polarity of C+- CI -

C - Br ᵟ+ ᵟ-

electron

Electron deficient carbon

OH ..

ᵟ- ᵟ+

Nucleophilic Substitution rxn

CH3CH2CI + OH- → CH3CH2OH + CI-

H H

׀ ׀

H - C – C – CI

׀ ׀

H H

+ OH- ᵟ+ ᵟ-

H H

׀ ׀

H - C – C – OH + CI-

׀ ׀

H H

H Br H

׀ ׀ ׀

H - C – C – C – H

׀ ׀ ׀

H H H

CH3CHBrCH3 + OH- → CH3CHOHCH3 + Br-

+ OH-

H OH H

׀ ׀ ׀

H - C – C – C – H + Br-

׀ ׀ ׀

H H H

ᵟ+ ᵟ-

Nucleophilic Substitution Electrophilic Addition

vs Reactivity of Alkene - High reactivity - Unstable bond bet C = C - High reactivity – Weak pi bond overlap bet p orbital - Unsaturated hydrocarbon – ᴨ bond overlap

C = C Electron rich π electron

ᵟ- ᵟ-

H ᵟ+

C = C ᵟ- ᵟ-

E ᵟ+

E+ Electron deficient Nu

ᵟ-

ᵟ-

Nucleophile – Lone pair electron – Donate electron pair - Lewis Base

H H ׀ ׀

C = C

׀ ׀ H H

CH2=CH2 + Br2 → CH2BrCH2Br

+ Br – Br ᵟ- ᵟ+

H H ׀ ׀

H - C – C – H

׀ ׀ Br Br

vs

CH2=CH2 + HCI → CH3CH2CI

H H ׀ ׀

C = C

׀ ׀ H H

ᵟ- + H – CI

ᵟ+

H H ׀ ׀

H - C – C – H

׀ ׀ H CI

Electrophilic Addition rxn

ᵟ-

Electron rich region

Electrophilic Substitution rxn

C6H6 + Br2 C6H5Br + HBr

+ Br-Br ᵟ+

+ NO2+

ᵟ+

Electrophilic Substitution

vs


ᵟ- ᵟ-

ᵟ+

C = C ᵟ- ᵟ-

E ᵟ+

E+ Electron deficient

E ᵟ+

H H ׀ ׀

C = C

׀ ׀ H H



H H ׀ ׀

H - C – C – H

׀ ׀ Br Br

vs


H H ׀ ׀

C = C

׀ ׀ H H

ᵟ- + H – CI ᵟ+

H H ׀ ׀

H - C – C – H

׀ ׀ H CI


E


ᵟ+ + H E

+ H


H Br

+ HBr

C6H6 + HNO3 C6H5NO2 + HCI

AICI3 dry ether

warm/conc H2SO4

H NO2

Reactivity of Alkene - High reactivity - Unstable bond bet C = C - High reactivity – Weak pi bond overlap bet p orbital - Unsaturated hydrocarbon – ᴨ bond overlap

Reactivity of Benzene (Unreactive) - Delocalization of electron in ring - Stability due to delocalized π electron - Substitution instead of Addition

C6H6 – no reaction with brown Br2(I)

ethene decolourize brown Br2(I)

Benzene –stable (unreactive) toward addition rxn


H

Electrophilic Addition


C - Br OH .. ᵟ- ᵟ+

Nucleophile Electrophile

ᵟ+

C = C ᵟ-


Organic Rxn

Addition rxn Substitution rxn

Nucleophilic Substitution

Free Radical Substitution

Electrophilic Substitution Electrophilic Addition rxn

Free radicle

CI CI

CI CI . .

:

Radical (unpair electron)

uv radiation

H H ׀ ׀

C = C

׀ ׀ H H

+ Br – Br

H H ׀ ׀

H - C – C – H

׀ ׀ Br Br

ᵟ+

ᵟ-

H H

׀ ׀

H - C – C – CI

׀ ׀

H H

+ OH-

H H

׀ ׀

H - C – C – OH + CI-

׀ ׀

H H

ᵟ- ᵟ+ H

E + + H

E ᵟ+

H H

׀ ׀

C = C

׀ ׀

H H

H H

׀ ׀

H - C – C – H

׀ ׀

CI CI

H H

׀ ׀

H - C – C – H

׀ ׀

H CI

H H

׀ ׀

H - C – C – H

׀ ׀

H OH

Add HCI

CI2 / UV

H H

׀ ׀

H - C – C – CI

׀ ׀

H H

H H

׀ ׀

H - C – C – OH + CI-

׀ ׀

H H

H H

׀ ׀

H - C – C – NH2 + CI-

׀ ׀

H H

H H

׀ ׀

H - C – C – CN + CI-

׀ ׀

H H

NH3

OH-

CN-

H

׀

H - C – H

׀

H

H

׀

H - C – CI + H

׀

H

CI2 → 2 CI•

CH3• + CI2 → CH3CI + CI•

CI• + CH4 → HCI + CH3•

H


C - Br OH .. ᵟ- ᵟ+

Nucleophile Electrophile

H ᵟ+

C = C ᵟ-


Free radicle

CI CI

CI CI . .

:

Radical (unpair electron)

uv radiation

H H

׀ ׀

C = C

׀ ׀

H H

H H

׀ ׀

H - C – C – H

׀ ׀

CI CI

H H

׀ ׀

H - C – C – H

׀ ׀

H CI

H H

׀ ׀

H - C – C – H

׀ ׀

H OH

Add HCI

CI2 / UV

H H

׀ ׀

H - C – C – CI

׀ ׀

H H

H H

׀ ׀

H - C – C – OH + CI-

׀ ׀

H H

H H

׀ ׀

H - C – C – NH2 + CI-

׀ ׀

H H

H H

׀ ׀

H - C – C – CN + CI-

׀ ׀

H H

NH3

OH-

CN-

H

׀

H - C – H

׀

H

H

׀

H - C – CI + H

׀

H

CI2 → 2 CI•

CH3• + CI2 → CH3CI + CI•

CI• + CH4 → HCI + CH3•

Alkene – Addition rxn Halogenoalkane – Substitution rxn Alkane - Radical substitution

H OH

׀ ׀

H - C – C – H

׀ ׀

H H

H O

‖ ׀

H - C – C – H

׀

H

H O

‖ ׀

H - C – C – OH

׀

H

H O H

׀ ‖ ׀

H - C – C – C – H

׀ ׀

H H

H OH H

׀ ׀ ׀

H - C – C – C – H

׀ ׀ ׀

H H H

H OH H

׀ ׀ ׀

H - C – C – C – H

׀ ׀ ׀

H CH3 H

Alcohol – Oxidation rxn

10 alcohol 20 alcohol 30 alcohol

carboxylic acid aldehyde ketone

no reaction




ᵟ- ᵟ- Br ᵟ+

H H ׀ ׀

C = C

׀ ׀ H H

+ H – Br ᵟ- ᵟ+

H H ׀ ׀

H - C – C – H

+ ׀ H

Electrophilic Addition

Symmetrical Alkene

HBr polar

CH2=CH2 + HBr → CH3CH2Br

: Br-

H H ׀ ׀

H - C – C – H

׀ ׀ H Br


Electrophilic addition to symmetrical alkene

H H ׀ ׀

C = C

׀ ׀ H H

+ Br – Br ᵟ+ ᵟ-

Br2 non polar : induced dipole due to C=C

H H ׀ ׀

H - C – C – H

+ ׀ Br

: Br-

H H ׀ ׀

H - C – C – H

׀ ׀ Br Br

carbocation

carbocation

Heterolytic fission

Heterolytic fission

CH2=CH2 + Br2/H2O → CH2BrCH2Br

H H ׀ ׀

C = C

׀ ׀ H H

+ Br – Br

Heterolytic fission

ᵟ+ ᵟ-

H H ׀ ׀

H - C – C – H

+ ׀ Br

: Br-

H H ׀ ׀

H - C – C – H

׀ ׀ Br Br

H H ׀ ׀

H - C – C – H

+ ׀ Br

: OH- from

H2O

H H ׀ ׀

H - C – C – H

׀ ׀ Br OH

H H ׀ ׀

C = C

׀ ׀ H H

H H ׀ ׀

CH3 – C = C – CH3

+ H – Br

H H ׀ ׀

H - C – C – H

׀ ׀ H Br

+ H – Br

H H ׀ ׀

CH3 – C – C – CH3

׀ ׀ H Br

only 1 product

H CH3

׀ ׀

H – C = C – H

Asymmetrical Alkene

+ H – Br

H CH3

׀ ׀

H – C – C – H

׀ ׀

H Br

H CH3

׀ ׀

H – C – C – H

׀ ׀

Br H

carbocation

2 product

H H ׀ ׀

C = C

׀ ׀ H H

+ H – Br ᵟ- ᵟ+

H H ׀ ׀

H - C – C – H

+ ׀ H

HBr polar

CH2=CH2 + HBr → CH3CH2Br

: Br-

H H ׀ ׀

H - C – C – H

׀ ׀ H Br


Addition to symmetrical alkene

H H ׀ ׀

C = C

׀ ׀ H H

+ Br – Br ᵟ+ ᵟ-

Br2 non polar : induced dipole due to C=C

H H ׀ ׀

H - C – C – H

+ ׀ Br

: Br-

H H ׀ ׀

H - C – C – H

׀ ׀ Br Br

carbocation

Heterolytic fission

Heterolytic fission

CH2=CH2 + Br2/H2O → CH2BrCH2Br

H H ׀ ׀

C = C

׀ ׀ H H

+ Br – Br

Heterolytic fission

ᵟ+ ᵟ-

H H ׀ ׀

H - C – C – H

+ ׀ Br

: Br-

H H ׀ ׀

H - C – C – H

׀ ׀ Br Br

H H ׀ ׀

H - C – C – H

+ ׀ Br

: OH- from

H2O

H H ׀ ׀

H - C – C – H

׀ ׀ Br OH

H CH3

׀ ׀

H – C = C – H + H – Br

H CH3

׀ ׀

H – C – C – H

׀ ׀

H Br

H CH3

׀ ׀

H – C – C – H

׀ ׀

Br H

Addition to asymmetrical alkene

CH2=CHCH3 + HBr → CH3CHBrCH3 or CH2BrCH2CH3

major

minor

CH3 CH3

׀ ׀

H – C = C – CH3 + H – Br

CH3 CH3

׀ ׀

H – C – C – H

׀ ׀

H Br

CH3 CH3

׀ ׀

H – C – C – H

׀ ׀

Br H

major

minor

✓

✓

Markovnokov rule - Hydrogen/electrophile add to carbon with most H2 bonded - Due to stable carbocation intermediate formed

R

׀

R – C +

׀

R

H

׀

R – C +

׀

R

H

׀

H – C +

׀

R

H

׀

H – C +

׀

H

30 carbocation

> > >

20 carbocation 10 carbocation

H CH3

׀ ׀

H – C ← C – H

׀ +

H

H CH3

↓ ׀

H – C → C – H

+ ׀

H

+ H – Br ᵟ- ᵟ+

: Br-

: Br-

2 alkyl gp – positive inductive effect – push electron to carbocation (more stable)

Heterolytic fission H CH3

׀ ׀

H – C = C – H


CH2=CHCH3 + HBr → CH3CHBrCH3

major

minor

CH3 CH3

׀ ׀

H – C = C–CH3 + H – Br

CH3 CH3

↓ ׀

H – C → C ← CH3

+ ׀

H

CH3 CH3

׀ ↓

H – C ← C – CH3

׀ +

H

major

minor

✓

✓

Markovnokov rule - H add to carbon with most H2 bonded - Due to stable carbocation formed

R

׀

R – C +

׀

R

H

׀

R – C +

׀

R

H

׀

H – C +

׀

R

> >

H CH3

׀ ׀

H – C – C – H

׀ ׀

H Br

H CH3

׀ ׀

H – C – C – H

׀ ׀

Br H

1 alkyl gp – positive inductive effect – push electron to carbocation (less stable)

ᵟ+ ᵟ -

: Br-

CH3 CH3

׀ ׀

H – C – C – CH3

׀ ׀

H Br


: Br-

2 alkyl gp – positive inductive effect – push electron to carbocation (less stable)

CH3 CH3

׀ ׀

H – C – C – CH3

׀ ׀

Br H

30 carbocation

most stable

10 carbocation

least stable

H CH3

↓ ׀

H – C → C – H

+ ׀

H

H CH3

׀ ׀

H – C ← C – H

׀ +

H

>

20 carbocation – greater positive inductive effect - more stable/lower charge density carbocation

CH3 CH3

↓ ׀

H – C → C ← CH3

+ ׀

H

>

CH3 CH3

׀ ↓

H – C ← C – CH3

׀ +

H


H CH3

׀ ׀

H – C ← C – H

׀ +

Br

H CH3

↓ ׀

H – C → C – H

+ ׀

Br

+ Br – CI ᵟ- ᵟ+

: CI-

: CI-


Heterolytic fission H CH3

׀ ׀

H – C = C – H


CH2=CHCH3 + BrCI → CH2BrCHCICH3

major

minor

CH3 CH3

׀ ׀

H – C = C–CH3 + I – CI

CH3 CH3

↓ ׀

H – C → C ← CH3

+ ׀

I

CH3 CH3

׀ ↓

H – C ← C – CH3

׀ +

I

major

minor

✓

✓

Markovnokov rule - H add to carbon with most H2 bonded - Due to stable carbocation formed

R

׀

R – C +

׀

R

H

׀

R – C +

׀

R

H

׀

H – C +

׀

R

> >

H CH3

׀ ׀

H – C – C – H

׀ ׀

Br CI

H CH3

׀ ׀

H – C – C – H

׀ ׀

CI Br

1 alkyl gp – less positive inductive effect – (less stable)

ᵟ+ ᵟ -

: CI-

CH3 CH3

׀ ׀

H – C – C – CH3

׀ ׀

I CI


: CI-

2 alkyl gp – less positive inductive effect – (less stable)

CH3 CH3

׀ ׀

H – C – C – CH3

׀ ׀

CI I

30 carbocation

most stable

10 carbocation

least stable

H CH3

↓ ׀

H – C → C – H

+ ׀

Br

H CH3

׀ ׀

H – C ← C – H

׀ +

Br

>


CH3 CH3

↓ ׀

H – C → C ← CH3

+ ׀

I

>

CH3 CH3

׀ ↓

H – C ← C – CH3

׀ +

I


EN CI higher

EN CI higher

ᵟ-


Electrophilic Substitution rxn

C6H6 + Br2 C6H5Br + HBr

+ Br-Br ᵟ+

+ NO2+

ᵟ+

Electrophilic Substitution Electrophilic Addition

vs


ᵟ- ᵟ-

ᵟ+

C = C ᵟ- ᵟ-

E ᵟ+

E+ Electron deficient

E ᵟ+

H H ׀ ׀

C = C

׀ ׀ H H



H H ׀ ׀

H - C – C – H

׀ ׀ Br Br

vs


H H ׀ ׀

C = C

׀ ׀ H H

ᵟ- + H – CI ᵟ+

H H ׀ ׀

H - C – C – H

׀ ׀ H CI


E


ᵟ+ + H E

+ H


H Br

+ HBr

C6H6 + HNO3 C6H5NO2 + HCI

AICI3 dry ether

warm/Conc H2SO4

H NO2



C6H6 – no reaction with brown Br2(I)

ethene decolourize brown Br2(I)

Benzene –stable (unreactive) toward addition rxn


H


Cyclohexene (Addition) vs Benzene (Substitution)

✓

Positive charge distributed in benzene ring (carbocation intermediate)

Benzene highly unreactive to addition rxn

: Br- +

+ Br – Br

+ Br – Br AICI3 dry ether

Benzene undergo substitution rxn

Cyclohexene undergo addition rxn

Benzene undergo electrophilic substitution (Bromination)

Loss H+ enable aromatic ring to reform

Br - Br

Br Br

Benzene undergo electrophilic substitution (Nitration)

+NO2

NO2 NO2

Positive charge distributed in benzene ring (carbocation intermediate)

Loss H+ enable aromatic ring to reform C6H6 + HNO3 C6H5NO2

Conc H2SO4

50C

Conc HNO3 + H2SO4 produce NO2+ electrophile

+

H


Electrophilic Substitution

H

E ᵟ+

+ + H

E


C6H6 + Br2 C6H5Br + HBr AICI3 dry ether

H

+ Br-Br ᵟ+

+ HBr Br

✓

OH O

‖ ׀

CH3-C–CH3 + [O] CH3- C– CH3

H

׀

CH3-CH2-OH + [O] CH3- C = O

Reduction rxn Oxidation rxn

MnO4- /H

+

K2Cr2O7/H+

10 Alcohol – Oxidised to Aldehyde and Carboxylic acid

20 Alcohol - Oxidised to Ketone

MnO4- /H

+

K2Cr2O7/H+

MnO4- /H

+

K2Cr2O7/H+

Oxidation vs Reduction rxn

O

‖

CH3-COH

Oxidation of Alcohol Acidified dichromate(VI)/permanganate(VII)

Reduction carbonyl (C = O) Sodium borohydride (NaBH4)

Lithium aluminium hydride (LiAIH4) / dry ether

O

‖

CH3-COH CH3CHO CH3CH2OH

O OH

׀ ‖

CH3-C–CH3 CH3- C– CH3

[H-] [H-]

NaBH4 NaBH4

Carboxylic acid reduced to aldehyde / alcohol

NaBH4

[H-]

Ketone reduced to alcohol

Hydride ion (nucleophile) :H-

produce

hydride ion / :H-

O

‖

CH3-COH CH3CH2OH

Carboxylic acid reduced alcohol

[H-]

LiAIH4 dry ether with acid

stronger reducing agent

Sn / conc HCI / reflux

Nitrobenzene reduced to phenylamine

NH3+ NO2

NH2

NaOH

phenylammonium

ion

reducing agent

Convert benzene to phenylamine

Convert propanoic acid to propanol

Convert ethanal to ethanol

O

‖

CH3CH2 COH CH3CH2CH2OH [H-]

stronger reducing agent

LiAIH4 dry ether / acid

CH3CHO CH3CH2OH [H-]

NaBH4

50C

NO2

conc HNO3 + H2SO4 Sn / conc HCI / reflux

NH3+

NaOH

NH2

׀ ׀ C - C –OH ׀ ׀

O ‖ C – C – C

O ‖ C – C – H

O ‖ C – C – OH

O ‖ C –C – C– O – C – C

No reaction

1o alcohol

[O]/Cr2O7/H+

Aldehyde

Ketone

Carboxylic Acid

Free radical substitution

CI2/ UV

Halogenoalkane

Alkane

2o alcohol

[O]/ Cr2O7/H+

[O]/ Cr2O7/H+

3o alcohol

[O]/ Cr2O7/H+

Substitution

warm / OH-

Alcohol

Alcohol Alkene

Elimination

100C /Conc alcoholic OH-

Alkane Halogenoalkane Dihalogenoalkane

Condensation

Ester

Addition

Polymerisation

X

׀ ׀ C – C – CI ׀ ׀

׀ ׀ C = C ׀ ׀

׀ ׀ ׀ ׀ C – C – C – C ׀ ׀ ׀ ׀

׀ ׀ C – C ׀ ׀ H CI

׀ ׀ C – C ׀ ׀ CI CI

׀ ׀ C – C ׀ ׀ Br Br

׀ ׀ C – C ׀ ׀

׀ ׀ C – C – OH ׀ ׀

Start here

PolyAlkene

׀ ׀ C – C ׀ ׀ H H

[H]/ NaBH4 [H]/ NaBH4

[H]/ NaBH4

oxidation

reduction

oxidation

oxidation

reduction

reduction

conc HNO3 / H2SO4

50C

NO2


NH3+

NaOH

NH2

C – C = C – C → C – C – C – C ‖

O

Synthetic routes

C –C –C – I → C – C – C-H ‖

O

Two steps 1 - Addition of H2O 2 - Oxidation alcohol to ketone

Two steps 1 – Substitution with OH- to alcohol 2 - Oxidation alcohol to aldehyde

But-2-ene to Butanone 1-iodopropane to propanal

1-chloropropane to propanoic acid

C –C –C –CI → C – C–COOH

Three steps 1 – Substitution with OH- to alcohol 2 - Oxidation alcohol to aldehyde 3 - Oxidation aldehyde to carboxylic acid

C – C = C – C

C – C – C – C ׀ ׀

H OH

C – C – C – C ‖

O

H2O /300C

H2SO4 catalyst [O] oxidation

K2Cr2O7/H+

C – C – C – I C – C – C – H ‖

O

C – C – C–OH

warm NaOH

SN2

[O] oxidation

K2Cr2O7/H+

C – C – C – CI C – C – COOH

C – C – C–OH C – C – C – H ‖ O

warm NaOH

SN2

[O] oxidation

K2Cr2O7/H+

Propane to propanoic acid

C –C –C → C –C –COOH

C – C – C C – C – COOH

C – C – C–CI C – C – C–OH

[O] oxidation

K2Cr2O7/H+

reflux

Warm NaOH

SN2

Free radical

substitution

UV / CI2

Three steps 1 – Free radical substitution to halogenoalkane 2 – Substitution with OH- to alcohol 3 – Oxidation alcohol to carboxylic acid

[O] oxidation

K2Cr2O7/H+

reflux

Synthetic routes Propane to propyl propanoate

Butene to butanone

Three steps 1 – Addition HBr 2 – Substitution with OH –

3 – Oxidation of alcohol to ketone

Four steps 1 – Free radical substitution/UV 2 – Substitution with OH -

3 – Oxidation alcohol to carboxylic acid 4 – Esterification with conc acid

Ethene to ethanoic acid

C – C

׀ ׀

H OH

C – C – H ‖

O

C – COOH

Three steps 1 – Addition using H2O 2 - Oxidation alcohol to aldehyde 3 – Oxidation aldehyde to carboxylic acid

Ethanol to ethyl ethanoate

C – C-OH → C–COO–C–C

C – C – O – C – C

‖

O

C–C–OH

C – COOH

Esterification

Ethanol + ethanoic acid

Conc H2SO4

Two steps 1 – Oxidation alcohol to carboxylic acid 2 – Esterification with ethanol/conc acid

C = C → C – COOH

Free radical

substitution

UV / CI2

C–C–C–CI

C – C – C

C–C–C–OH Warm NaOH

SN2

C–C–COOH [O] oxidation/reflux

K2Cr2O7/H+

C – C – C – O – C – C – C

‖

O Esterification

Propanol + propanoic acid

Conc H2SO4

C – C = C – C C – C – C – C ‖ O Addition HBr

C – C – C – C ׀ ׀

Br H Warm NaOH

SN2

C – C – C – C ׀ ׀

OH H

[O] oxidation

K2Cr2O7/H+

[O] oxidation

K2Cr2O7/H+

reflux

C – C = C – C → C – C – C – C ‖

O

C = C

H2O /300C

H2SO4 catalyst

[O] oxidation

K2Cr2O7/H+

[O] oxidation

K2Cr2O7/H+

reflux

C – C – C → C – C – C –O–C–C–C ‖

O

Synthetic routes

Benzene to phenylamine

Ethanoic acid to ethyl ethanoate

Two steps 1 – Reduction to alcohol 2 – Esterification with ethanoic acid/conc acid

C – COOH

C–C–OH

Three steps 1 – Nitration substitution of benzene 2 – Reduction of nitrobenzene 3 – Addition NaOH

Ethanoic acid to ethanol

C – C

׀ ׀

H OH

C – C – H ‖

O

C – COOH

Two steps 1 – Reduction acid to aldehyde 2 - Reduction aldehyde to alcohol

C – COOH → C –COO–C–C

C – C – O – C – C

‖

O

Reduction [H-]

LiAIH4 dry ether

acid

Esterification

Ethanol + ethanoic acid

Conc H2SO4

Ethane to Ethanol

C – C → C–C-OH

C – C

C – C – CI

Two steps 1 – Free radical substitution/UV 2 – Substitution with OH-

NO2

NH2

NH2

NH3+

conc HNO3

conc H2SO4 50C


NaOH

C – COOH → C – C-OH

Reduction [H-]

NaBH4

Reduction [H-]

NaBH4

Free radical

substitution

UV / CI2

C – C

׀ ׀

H OH

warm NaOH

SN2

IB Chemistry on Electrophilic Addition and Synthetic routes

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Transcript of IB Chemistry on Electrophilic Addition and Synthetic routes