Why aryl halides undergo electrophilic substitution reactions at o - and p - position ? Why it is less reactive than benzene ?

Explanation

Haloarenes undergo electrophilic reactions of the benzene ring such as halogenation, nitration, sulphonation and Friedel - Crafts reactions. Halogen atom being slightly deactivating is o, p - directing, therefore, further substitution occurs at o - and p - positions with respect to halogen.

Due to resonance, the electron density increases more at ortho - and para - positions than at meta - positions.
The aryl halides are less reactive than benzene towards electrohilic substitution reactions because the ring it some what deactivated due to `-I` effect of halogens that shows tendency to withdraw electrons from benzene ring. So electrophilic substitution reactions in a haloarenes requires more drastic conditions.