Consider the structures given below.Which of them would be a relatively stable contributor to the hybrid formed when toluene undergoes para bromination?
A)I
B)II
C)III
D)IV

Question

Consider the structures given below.Which of them would be a relatively stable contributor to the hybrid formed when toluene undergoes para bromination? 
A)I 
B)II 
C)III 
D)IV

Quizplus · Accepted Answer

Para-bromination of toluene results in the formation of a resonance hybrid since the phenyl ring is highly conjugated system. Resonance stabilizes the intermediate formed during the mechanism of the halogenation. 
Among the given resonance structures, III is the most stable contributor. This is because in structure III, the positive charge is mainly localized on the carbon attached to the bromine. In contrast, in other structures, the positive charge is mainly delocalized over the ring, which reduces its contribution to the overall resonance-stabilized intermediate.

Consider the Structures Given Below