Saeed Anwar Lecturer in Chemistry
Government College Peshawar Pakistan
E-mail:
Contact: +923025126034
Class Notes-XII…Organic Chemistry
BENZENE AND SUBSTITUTED BENZENES
BENZENE
Benzene is the simplest member of aromatic hydrocarbons having molecular formula C6H6.
Benzene has six carbons and six hydrogens having alternate single and double bonds between
the six carbon atoms. When one hydrogen atom is replaced by a substituent, it is called mono
substituted benzene. When two hydrogen atoms are replaced by substituents, it is called
disubstituted benzene. When more than two hydrogen atoms are replaced, these are called
polysubstituted benzene. Following is the structural formula of benzene.
H
H H
H H
Benzene
H
Nomenclature of Benzene
There are two systems of nomenclature. One is called common system and other is called
IUPAC system. Common names have been written in brackets while IUPAC names written
below the common names.
Mono substituted benzenes
, F Cl Br I
Flourobenzene Chlorobenzene Bromobenzene Iodobenzene
Some mono substituted benzenes have special commercial names which have been shown
below;
CH3 OH NH2 COOH
Toluene Phenol Aniline Benzoic acid
Disubstituted benzenes
When there are two substituents are present on the benzene ring, three possible isomers are
obtained, called ortho (o-), meta (m-) and para (p-) isomers. Common names have been
written in brackets.
, Br
CH3 Br Br
6 1 2
Br
1 6 1 2 1
ortho6 2 6 2
ortho
5 4 3
3
meta 5 3 meta 5 3 5
Br
4 4 4 Br
para
(Toluene) (o-Dibromobenzene) (m-Dibromobenzene) (p-Dibromobenzene)
1-Methylbenzene 1,2-Dibromobenzene 1,3-Dibromobenzene 1,4-Dibromobenzene
Cl
CH3
CH3 CH3 Br
6 1 2
6 1 2
CH3
6 1 2 1
6 2
5 3
5 4 3
4
3
5 3 5
CH3
4 4 CH3
(o-Xylene) (m-Xylene) (p-Xylene) o-Bromochlorobenzene)
1,2-Dimethylbenzene 1,3-Dimethylbenzene 1,4-Dimethylbenzene 2-Bromo-1-chlorobenzene
OH OH OH
OH
6 1 2 1 1
6 2 6 2
3
5 3 5 5 3
4
4
OH
4
(Catechol) (Resorcinol) (Hydroquinone)
1,2-Dihydroxybenzene 1,3-Dihydroxybenzene OH 1,4-Dihydroxybenzene
If the substituents are different, they are named alphabetically. Common names have been
written in brackets and IUPAC names written below the common names. For example,
Government College Peshawar Pakistan
E-mail:
Contact: +923025126034
Class Notes-XII…Organic Chemistry
BENZENE AND SUBSTITUTED BENZENES
BENZENE
Benzene is the simplest member of aromatic hydrocarbons having molecular formula C6H6.
Benzene has six carbons and six hydrogens having alternate single and double bonds between
the six carbon atoms. When one hydrogen atom is replaced by a substituent, it is called mono
substituted benzene. When two hydrogen atoms are replaced by substituents, it is called
disubstituted benzene. When more than two hydrogen atoms are replaced, these are called
polysubstituted benzene. Following is the structural formula of benzene.
H
H H
H H
Benzene
H
Nomenclature of Benzene
There are two systems of nomenclature. One is called common system and other is called
IUPAC system. Common names have been written in brackets while IUPAC names written
below the common names.
Mono substituted benzenes
, F Cl Br I
Flourobenzene Chlorobenzene Bromobenzene Iodobenzene
Some mono substituted benzenes have special commercial names which have been shown
below;
CH3 OH NH2 COOH
Toluene Phenol Aniline Benzoic acid
Disubstituted benzenes
When there are two substituents are present on the benzene ring, three possible isomers are
obtained, called ortho (o-), meta (m-) and para (p-) isomers. Common names have been
written in brackets.
, Br
CH3 Br Br
6 1 2
Br
1 6 1 2 1
ortho6 2 6 2
ortho
5 4 3
3
meta 5 3 meta 5 3 5
Br
4 4 4 Br
para
(Toluene) (o-Dibromobenzene) (m-Dibromobenzene) (p-Dibromobenzene)
1-Methylbenzene 1,2-Dibromobenzene 1,3-Dibromobenzene 1,4-Dibromobenzene
Cl
CH3
CH3 CH3 Br
6 1 2
6 1 2
CH3
6 1 2 1
6 2
5 3
5 4 3
4
3
5 3 5
CH3
4 4 CH3
(o-Xylene) (m-Xylene) (p-Xylene) o-Bromochlorobenzene)
1,2-Dimethylbenzene 1,3-Dimethylbenzene 1,4-Dimethylbenzene 2-Bromo-1-chlorobenzene
OH OH OH
OH
6 1 2 1 1
6 2 6 2
3
5 3 5 5 3
4
4
OH
4
(Catechol) (Resorcinol) (Hydroquinone)
1,2-Dihydroxybenzene 1,3-Dihydroxybenzene OH 1,4-Dihydroxybenzene
If the substituents are different, they are named alphabetically. Common names have been
written in brackets and IUPAC names written below the common names. For example,
