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 are less reactive towards nucleophilic substitution reactions due to the partial double bond character between the carbon and halogen in the aromatic ring, which makes it harder for the halogen to leave. The presence of a nitro group (\(-\text{NO}_2\)) at the ortho- or para-positions on the benzene ring activates the ring towards nucleophilic substitution. The nitro group is electron-withdrawing, which increases the positive character of the carbon attached to the halogen, making it more susceptible to attack by nucleophiles.