Q12 P - Organic Chemistry (Mcmurry)

Question

Acetanilide is less reactive than aniline toward electrophilic substitution. Explain

Step-by-Step Solution

Answer

Since the nitrogen lone pairs are less available to the ring than in aniline, the reactivity of ring towards electrophilic substitution reduces, and acetanilide becomes less reactive than aniline towards electrophilic substitution

Step 1: Ortho and para directing activators

Inductive and resonance effects account for the orientation of electrophilic aromatic substitution. All the three intermediates, ortho,meta and para are resonance stabilized. However the ortho and para intermediates have significant stability than the meta intermediate.

Step 2: Reactivity of acetanilide and aniline towards electrophilc substitution

                               Less favored delocalization

                        More favored delocalization

 

For acetanilide, the resonance delocalization of the nitrogen lone pair to the aromatic ring is less favored as the positive charge on nitrogen is next to the positively polarized carbonyl group. Resonance delocalization to the carbonyl oxygen is favored due to the electronegativity of oxygen. Since the nitrogen lone pairs are less available to the ring than in aniline, the reactivity of ring towards electrophilic substitution reduces, and acetanilide becomes less reactive than aniline towards electrophilic substitution.