Post on 13-Apr-2017
Hydrocarbons
Those compounds which contain only carbon
and hydrogen.
There are two types of hydrocarbons:
1- saturated hydrocarbons: in which all
carbon bonds are sigma (σ)bonds,
include alkanes and cycloalkanes.
2- unsaturated hydrocarbons: which contain sigma
as well as pi-bonds, include alkenes (paraffin) and
Alkynes (acetylenes).
Nomenclature of organic compounds:
The IUPAC rules for alkanes
1.The general name for acyclic saturated hydrocarbon is Alkanes. The – ane ending is used for all saturated hydrocarbons
2: alkanes without branches are named according to the number of carbon atoms.
CH4 MethaneCH3CH3 EthaneCH3CH2CH3 PropaneCH3(CH2)2CH3 n- butaneCH3(CH2)3CH3 n- pentaneCH3(CH2)4CH3 n- hexaneCH3(CH2)5CH3 n- heptaneCH3(CH2)6CH3 n- octane CH3(CH2)7CH3 n- None
3: for alkanes with branched chains, the root name
Is that of the longest continuous chain of carbon atoms, for example
CH3CH CHCH2CH3
CH3CH3
The longest continuous chain (colored C’s) has five carbon atoms .the compound is therefore named as substituted pentane.
4: Groups attached to the main chain are called substituents. Saturated substituens that contain only carbon and hydrogen called alkyl groups
Alkyl groups
- CH3 Methyl
- CH2CH3 Ethyl
- CH2CH2CH3 n-Propyl
CH3CHCH3 isopropyl
Other substituent• -OH• -NO2
• -OCH3
• -CN• -Cl• -Br• -F• -I• -NH2
• Hydroxy• Nitro• Methoxy• Cyano• Chloro• Bromo• Flouro• Iodo• Amino
In the example, each branch has only one carbon. derived from the hydrocarbon methane by removing one of the hydrogens, it is called the methyl group.
CH3- or Me-
5: groups are located by a name and number.
The main chain is numbered in such a way that the first substituent receive the lowest possible number.
`
CH3 CH CH CH2 CH3
CH3 CH3
1 2 3 4 5
When two identical groups are attach to the main chain, prefixes such as di, tri, and tetra- are used.
The previous compound is correctly named as 2,3 - dimethylpentane
6: Punctuation is important in writing IUPAC names .The names are written as one word. Numbers are separated from each other by commas and from letters by hyphens.
If two or more different types of substituents are present, they are listed alphabetically, except that prefixes such as di- and tri- are not counted for alphabetizing.
Examples:
Give the IUPAC name for the following compounds.
A: CH3 CH CH2 CH3
CH3 CH3
B: CH3 CH2 CH CH3 C: CH3– C-CH3
NO2 CH3
D) CH3C(CH3)3 E) BrCH2CH2CHCl2
Cycloalkanes
Carbocyclic hydrocarbons that are named by placing the prefix cyclo- before the alkane name corresponding to the number of carbon atoms in the ring.
Cyclopropane cyclobutane cyclopentane
Cyclohexane cyclooctane
When the ring carry alkyl or halogen substituents, they are named in the usual way.
CH3 CH3 CH3 CH3
CH3
Methylcyclopropane 1,1-dimethylcyclopentane 1,2-dimethylcyclopentane
Alkenes
are hydrocarbons that contain one
double bond, When the molecule contain
two double bonds it is often called a diene
CH2=CH2 Ethene (ethylene)
CH2=CH-CH3 Propene
CH2=CH-CH2-CH3 Butene-1
CH3-CH=CH-CH3 Butene-2
cyclopentene
CH3
3-methylcyclohexene
CH3
1-methylcyclopentene
Preparation of alkenes
The most used methods for preparations of alkenes and alkynes are based on elimination reactions
C C
Y Z
eliminationC C
alkene
1- dehydrogenation This reaction includes removal of hydrogen from saturated hydrocarbons in presence of a catalyst and at high temperature e.g
CH3
CH3Cr2O3/Al2O3
CH3
CH3+ CH2
CH3
+ H2
2-dehalogenation
The reaction includes removal of halogen of 1,2- dihalogen derivatives of alkanes by means of Zn dust and methanol
CHBr
CH3
BrH2C
ZnCH3OH CH3-CH=CH2 + ZnBr2
3- Dehydration:
Dehydration of secondary and tertiary alcohol using dilute sulphuric acid
CH3CH2CHOHCH3 CH3CH=CHCH3 + H2O
4- Dehydrohalogenation
By the action of ethanolic potassium hydroxide on alkyl halides, eg propene from propyl bromide
CH3CHBrCH3 CH2=CHCH3
CH3CH2CHBrCH3 CH3CH=CHCH3
KOH
KOH
Chemical properties of alkenes
Owing to the presence of the double bond
the alkenes undergo addition reactions
C = C + E – Nu C+ CE
CNu CE
1-Hydrogenation
Alkenes are hydrogenated under
pressure of hydrogen at the presence
of a catalyst
CH2 = CH2 + H2 CH3 - CH3
catalyst
2- Hydration
Alkenes are catalytically hydrated in dilute acid solution giving alcohols
CH3CH =CH2 + H2O CH3CHOHCH3H+
3- Halogenation Chlorine and bromine are readily adde to the double bond in the dark
CH2 = CH2 + Br2 CH2Br – CH2Br
alkynesNomenclatures
Alkynes
Name Formula Structural Formula
Ethyne (Acetylene)
C2H2 CH ≡CH
Propyne C3H4 CH≡ C-CH3
1-Butyne C4H6 CH≡ C-CH2-CH3
2-Butyne C4H6 CH3-C≡ C-CH3
General methods for preparation of alkynes
1- By the action of potassium hydroxide on gem or Vicinal dihalide the reaction proceeds in two steps
BrCH2CH2Br + KOH CH2=CHBr
CH2= CHBr + KOH CH≡CH+2KBr+H2O Acetylene
ethanol
ethanol
2- Dehalogenation
By the action of zinc dust and heat on tetrahalogeno alkanes
CH3CBr2-CHBr2 + 2 Zn CH3 – C≡ CHHeat -2ZnBr2
Chemical properties of alkynes :
Undergo the same reaction as alkenes but using two moles of the reagent
1- CH3C = CH CH3CH2CH3
Propyne n- propane
2- CH = CH + Cl2CH-CHCl2
3- CH3C = CH CH3CBr2CH3
2H2/Pd
2HBr
2Cl2
Aromatic hydrocarbons
Aromatic are cyclic, they are unsaturated,
usually have three conjugated double bonds for
each ring of carbon atoms , not all aromatic are
hydrocarbon e.g pyridine
N
Pyridine
Benzene
Benzene is the an example for aromatic
hydrocarbons.
Benzene has six pi electrons two from each
of the double bonds
benzene
Fused ring system
Those are aromatic similar to benzene with more
than one benzene ring e.g naphthalein and
anthracene
naphthaleneanthracene
Substituted benzene
The benzene ring minus one hydrogen (C6H5-)
is named as phenyl group. In general group
derived from aromatic compounds by removing
One hydrogen from carbon called aryl group.
When one hydrogen replaced by other group is
called monosubstituted
Cl CH3O OH O H
NH2
O NH2OCH3
chlorobenzene benzoic acid benzaldehyde
aniline benzamide anisole
toluene
ClCl
CH3CH3
O OH
OH
o-xylene1,2-dichlorobenzene
2-hydroxybenzoic acid
Reactions of Benzene •Benzene is always stable because of its delocalized (π) bonds. •Benzene is therefore chemically less reactive than unsaturated aliphatic hydrocarbons.
+ Br2F e B r2
Br
+ HBr
(1) Halogenation:
+ HNO3
NO2
+ H2OH 2S O 4
(2) Nitration:
(3) Sulphonation:
+
SO3H
+ H2OH 2S O 4 Benzene sulphonic acid
+
CH3
+ ClHCH3Cl
(4) Alkylation: