Question

Why are haloarenes less reactive towards nucleophilic substitution reactions? How does the presence of nitro (–NO₂) group at ortho- and para-positions in haloarenes increase the reactivity towards nucleophilic substitution reactions?

Hint:

Electron-withdrawing groups such as \(-\text{NO}_2\) increase the electrophilicity of the carbon attached to the halogen, making the compound more reactive towards nucleophilic attack.

Answer 1

Haloarenes exhibit reduced reactivity in nucleophilic substitution reactions. This is attributed to the partial double bond character between the carbon and halogen on the aromatic ring, hindering halogen departure. The presence of a nitro group (\(-\text{NO}_2\)) at ortho- or para-positions on the benzene ring enhances the ring's susceptibility to nucleophilic substitution. The electron-withdrawing nature of the nitro group increases the positive charge on the carbon bonded to the halogen, thereby increasing its electrophilicity and facilitating nucleophilic attack.