Question

Account for the following :

(a) Aniline does not undergo Friedel Crafts alkylation

(b) Although-NH₂ group is an ortho and para-directing group, nitration of aniline gives alongwith ortho and para-derivatives meta-derivative also.

Answer 1

(a) During Friedel Craft's alkylation, aluminium chloride acts as a catalyst, as well as a Lewis acid, if forms salt with– NH₂ group of aniline, so that–NH₂ group acquires a positive charge, and acts as a deactivating group, so aniline does not undergo FCA. 

(b) During nitration in strongly acidic medium aniline is protonated to form anilinium ion, which is a meta directing group, so along with o^– & p^– isomers, meta isomers is also obtained.