Question

Why does acetylation of –NH₂ group of aniline reduce its activating effect?

Answer 1

Direct nitration of aniline is not possible on account of oxidation of –NH₂ group. However, nitration can be carried after protecting the –NH₂ group by acetylation to give acetanilide which is then nitrated and finally hydrolysed to give o- and p-nitroanilines.

The acetyl group being electron-withdrawing attracts the lone pair of electrons of the N-atom towards carbonyl group.

As a result, the activating effect –NH₂ group is reduced i.e., the lone pair of electrons on nitrogen is less available for donation to benzene ring by resonance. Therefore, activating effect of –NHCOCH₃ group is less than that of –NH₂ group.