Chapter 23, Problem 23.48P

Interpretation Introduction

Interpretation:

The electrophilic aromatic substitution on $N,N\text{-dimethylaniline}$ is faster than on aniline; if both $N,N\text{-dimethylaniline}$ and aniline are methylated at $2$ and $6$ position, then methylated $N,N\text{-dimethylaniline}$ reacts slowly than methylated aniline. The difference in their reactivity is to be explained.

Concept introduction:

The alkyl groups have electron donating inductive effect which stabilizes the positive charge on the adjacent carbon. The electrophilic aromatic substitution reaction rate increases with increase in electron density around the ring. The electron donating groups activate the aromatic ring. The electron donating groups increase the electron density at ortho-para position, and thus, they are ortho-para directing. This means that electrophilic aromatic substitution preferably occurs at ortho-para position. The substitution at the ring carbons causes steric hindrance due to which the other group attached to the ring having lone pair no longer is in the ring plane and thus cannot participate in the conjugation. This decreases the electrophilic aromatic substitution rate of the ring.