Give reasons for the following observations:

Haloarenes are less reactive than haloalkanes towards nucleophilic substitution reaction.

The reason for the Haloarenes to be less reactive towards nucleophilic substitution reaction are as follows:

1. In the Haloarenes the molecule undergo resonance because of which the C-X bond in this molecule acquires a double bond character and hence it is difficult to break this bond.

2. In the haloalkanes, the hybridization of carbon atom is sp³ whereas in the Haloarenes the carbon atom is sp² hybridized. The sp2 hybridized carbon atom has more s-character because of which the electron pairs are more tightly held in the Haloarenes as compared to haloalkanes thus reducing the size of haloalkanes and making the Haloarenes stronger.

3. The phenyl cation which can be formed by the process of self-ionization is highly unstable and thus S_N1 mechanism is avoided.

4. Electron rich nucleophile when approaches the Haloarenes gets repelled away by the electron pairs of Haloarenes.