The presence of electron withdrawing group increases the reactivity of haloarenes towards nuncleophilic substitution reaction. Explain.

Explanation

Chlorobenzene can be converted into phenol by heating in aqueous NaOH at 623K and under a pressure of 300 atmosphere.

However in the presence of electron withdrawing group `(-NO_2)` at-o and p-positions the same hydrolysis can be carried out by warming with water only

This is because the electron withdrawing groups at o and p-positions stabilises the intermediate carbanion by resonance. However, no effect on reactivity of haloarenes is obeserved if the electron withdrawing group in present at m-position because in that case resonance stablisation of carbanion in not possible. This is clear from the mechanism of the reaction explained below.

As shown, the presence of `-NO_2` group at o and p-positions withdraws the electrons density from the benzene ring and thus lielps in the attack of nucleophile on haloarenes. The carbonian so formed is resonance stabilised. The -ve charge appeared at o and.p-positions w.rt. halogen is stabilised by `-NO_2` group. While in case of m-nitrochlorobenzene none of the resonating structure, bears the -ve charge an carbon atom bearing the `-NO_2` group. Therefore, the presence of `-NO_2` group at m-position does not disperse the-ve charge and no effect an reactivity is observed by the presence of `-NO_2` group at m-position