Which of the following compounds will undergo the fastest rate of electrophilic aromatic substitution when treated with ${\text{HNO}}_3/{\text{H}}_2{\text{SO}}_4$?

Solution

1. Electrophilic aromatic substitution rate depends on the electron density of the benzene ring.
2. The $-{\text{OCH}}_3$ group in anisole provides strong electron density via $+M$ effect.
3. The $-{\text{CH}}_3$ group in toluene provides electron density via $+I$ and hyperconjugation.
4. The $-{\text{NO}}_2$ group is strongly electron-withdrawing via $-M$ and $-I$ effects.
5. Hence the answer is (D).