Alkyl Chloride is more reactive than chlorobenzene towards nucleophilic substitution. Explain.

Explanation

Hydrolysis of alkyl or aryl halides is a nucleophilic substitution reaction. The lesser reactivity of haloarenes (say chlorobenzene) than haloalkanes (say chloromethane) in nucleophilic substitution reactions can be explained as follows: (i) Resonance effect: Haloarenes are resonance stabilised, For example, chlorobenzene is a resonance. hybrid of various contributing structures (I) to (V) as shown below:

As a result of resonance, in structure (IT) to (IV), C-Cl bond acquires some double bond character. On the other hand, no such resonance occurs in alkyl halides. Therefore, C-Cl bond in aryi halides is stronger than carbon-halogen bond in haloalkanes and hence can not be easily broken, so chlorobenzene is less reactive. (ii) Hybridisation of carbon bearing the halogen atom. In haloalkanes, the carbon atom attached to the halogen atom (C--X). is `sp^3` -hybridised whereas in haloarenes, the carbon atom attached to the halogen atom is `sp^2`-hybridised. Now `sp^2`-hybrid orbital of carbon is slightly smaller in size than the `sp^3`-hybrid orbital. Therefore, the nalogen bond in haloarenes is shorter and stronger than the carbon-halogen bond in haloalkanes. This also justify the low reactivity of haloarenes as compared to haloalkanes