( configurations ) of (i) CH CH CH CH Br < (CH ) CHCH Br < CH CH CH( Br )CH < (CH ) C Br (S N ) CH CH CH CH Br > (CH ) CHCH Br > CH CH CH( Br )CH > (CH ) C Br (S N ) Of the two primary bromides, the carbocation intermediate derived from (CH ) CHCH Br is more stable than derived from CH CH CH CH Br because of greater electron donating inductive effect of (CH ) CH- group. Therefore, (CH ) CHCH Br is more reactive than CH CH CH CH Br in S N reactions. CH CH CH(Br)CH is a secondary bromide and (CH ) CBr is a tertiary bromide. Hence the above order is followed in S N .
The reactivity in S N reactions follows the reverse order as the steric hinderance around the electrophilic carbon increases in that order. (ii) C H C(CH )(C H ) Br > C H CH(C H ) Br > C H CH(CH ) Br > C H CH Br (S N ) C H C(CH )(C H ) Br < C H CH(C H ) Br < C H CH(CH ) Br < C H CH Br (S N ) Of the two secondary bromides, the carbocation intermediate obtained from C H CH(C H ) Br is more stable than obtained from C H CH(CH ) Br because it is stabilised by two phenyl groups due to resonance. Therefore, the former bromide is more reactive than the latter in S N reactions. A