Question

The order of rate of electrophilic substitution reaction is:

• A. $Q>P>S>R$
• B. $Q>P>R>S$
• C. $P>Q>S>R$
• D. $P>Q>R>S$

Answer 1

Answer: (A)

$Q>P>S>R$

The rate of reaction of compound ($R$) is lower than that of compound ($S$) because, in compound ($R$), the amide group is directly attached to a benzene ring. It shows a negative resonance effect.
The rate of reaction of compounds ($P$) and ($Q$) are lower than that of compound ($S$) because in compounds ($P$) and ($Q$), the $-NHR$ or$-NHCOR$ group is directly attached to benzene ring through N atom. It shows a positive resonance effect.
Hence, the order of rate of electrophilic substitution reaction is $Q>P>S>R$.