Question

Why does side halogenation in alkyl benzenes takes place prefentially at positions alpha to the aromatic ring?​

Answer 1

Given: Side halogenation in alkyl benzenes

To find:

Why does side halogenation takes place preferentially at alpha position of aromatic ring?

Side chain halogenation takes place at alpha position because the intermediate benzylic free radicals are more stable and hence easily formed. The benzylic free radical formed from alkyl benzene has more resonance hybrid structures than primary free radical obtained from ethyl benzene.

 Due to its greater number of contributing structures benzylic free radical is more resonance stabilized than non benzylic free radical.

Therefore side halogenation in alkyl benzenes takes place preferentially at position alpha to aromatic ring.