Question
How will you explain the directive influence of halogens?
Solution
Halogens (Cl, Br, l) contain three pairs of electrons and thus release electrons to the aromatic ring through resonance. But due to its electrons withdrawing (-Inductive effect) nature, it also intensifies the positive charge on carbocation. Thus, inductive effect and resonance effect work in the opposite direction and the result of two opposing effects is electron withdrawal. That is why halogens deactivate the aromatic ring for electrophilic substitution. Consider chloro-benzene.+
Thus chlorine atom deactivates the ring due to -I effect and directs the incoming electrophile to attack at the ortho and para position due to resonance effect.
