Question

The correct order of reactivity towards the electrophilic substitution of the compounds aniline (I), benzene (II) and nitrobenzene (III) is

• A. II < III > I
• B. I > II > III
• C. III > II > I
• D. II > III > I

Answer 1

The Correct Option is B

The question asks us to determine the order of reactivity of the compounds aniline, benzene, and nitrobenzene towards electrophilic substitution reactions. To solve this, we need to consider how substituents on the benzene ring affect its reactivity towards electrophiles.

• Aniline (C₆H₅NH₂):
  • The amino group (-NH₂) in aniline is an electron-donating group due to resonance and the +I effect. It increases the electron density on the benzene ring, particularly at the ortho and para positions, making aniline highly reactive towards electrophiles.
• Benzene (C₆H₆):
  • Benzene, without any substituents that either donate or withdraw electrons, has a moderate level of reactivity. It serves as a standard for comparing reactivity.
• Nitrobenzene (C₆H₅NO₂):
  • The nitro group (-NO₂) is a powerful electron-withdrawing group due to its -I effect and resonance. It decreases the electron density on the benzene ring, making the ring less reactive towards electrophiles.

Based on the above analysis, the reactivity order towards electrophilic substitution reactions for these compounds is as follows:

1. Aniline is the most reactive because the amino group donates electrons to the benzene ring, increasing its reactivity.
2. Benzene is less reactive than aniline but more reactive than nitrobenzene as it lacks the electron-donating effect of aniline and the electron-withdrawing effect of nitrobenzene.
3. Nitrobenzene is the least reactive due to the strong electron-withdrawing effect of the nitro group, which decreases the electron density on the benzene ring.

Therefore, the correct order of reactivity is I > II > III.