AIPMT 2010 Physics and Chemistry Paper

Alkyl halides are more reactive toward nucleophilic substitution. Reactivity depends upon the stability carbocation intermediate formed.
Among the given halides, aryl halide (C6H5X) is least reactive towards nucleophile as in it the C−X bond acquire some double bond character due to resonance. Presence of electron withdrawing groups like −NO2 at ortho and para positions facilitate the nucleophilic displancent of −X of aryl halide. Among alkyl halides, 3∘ halides are more reactive as compared to 2∘ halides due to the formation of more stable carbocation. Hence, the order of reactivity of C−X bond towards nucleophile is as