Haloarenes are extremely less reactive to nucleophilic substitutions due to resonance stabilization of the molecule. The electron pairs on halogen atom are conjugated with ϖ-electrons of the aryl ring and the above resonating structures are possible. The C—X bond gains a partial double bond in resonance and thus it becomes difficult for cleavage of the bond, making is less reactive. There is also a difference in the hybridization of the carbon atom in the C—X bond. The carbon atom attached to halogen is sp2 hybridised unlike halloalkanes which are sp3 hybridised. The sp2 hybridised carbon holds the halogen more tightly, with a smaller bond length compared to the carbon atom attached to the halogen in sp3 hybridisation in haloalkane.
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