91Ó°ÊÓ

Isomers are molecules or polyatomic ions having identical molecular formulas but the distinct arrangement of atoms in space.

In organic chemistry ortho, meta and para are isomers of a compound generally cyclic in nature. They are used to indicate the position of non-hydrogen substituents on a hydrocarbon.

It is necessary to introduce substituents in the proper order when synthesizing substituted aromatic rings. A group that is introduced out of order will not have the proper directing effect.

Mostly in these types of reactions, a mixture of ortho and para isomer may be formed.

(a) Benzene reacts with chlorine molecule in the presence of Lewis acid to give chlorobenzene, which further participates in Friedel-Crafts acylation to produce p-Chloroacetophenone.

Benzenechlorobenzenep-Chloroacetophenone

(b) Benzene undergoes nitration to produce nitrobenzene which further reacts with bromine in the presence of FeBr₃ to synthesize m-bromonitrobenzene.

Benzene nitrobenzenem-Bromonitrobenzene

(c) Benzene undergoes bromination to produce bromobenzene, which further takes part in sulphonation reaction to produce o-Bromobenzenesulfonic acid

(d) Benzene undergoes sulphonation and then reacts with chlorine molecule to synthesize m-Chlorobenzenesulfonic acid.

Benzenebenzenesulfonic acid m-Chlorobenzenesulfonic acid