Question

Aniline does not undergo

• A. Nitration
• B. Sulphonation
• C. Friedel-Craft reaction
• D. Bromination

Answer 1

The Correct Option is C

Aniline (C6H5NH2) is a primary amine and exhibits certain reactivity patterns due to the presence of the amine group (-NH2), which is an electron-donating group. The electron-donating nature of the amine group makes the aromatic ring more reactive towards electrophilic substitution reactions. However, the amine group also affects its reactivity with certain reagents.

Analysis of the options:

• Option A: Friedel-Crafts reaction - Aniline does not undergo the Friedel-Crafts reaction effectively. This is because the amine group (-NH2) is a strong electron-donating group and reacts with the AlCl3 catalyst, which deactivates it and prevents the reaction. Hence, aniline does not undergo Friedel-Crafts reaction.
• Option B: Bromination - Aniline undergoes bromination readily, where the amine group activates the benzene ring and makes it more reactive towards electrophilic bromine (Br2) under mild conditions.
• Option C: Nitration - Aniline undergoes nitration readily, as the electron-donating nature of the amine group increases the electron density on the aromatic ring, making it more susceptible to electrophilic attack by the nitronium ion (NO2+).
• Option D: Sulphonation - Aniline also undergoes sulphonation, where the amine group activates the benzene ring towards electrophilic substitution by the sulfonic acid group (SO3H).

Conclusion:

Option A: Friedel-Crafts reaction, as aniline does not undergo Friedel-Crafts reactions due to deactivation of the catalyst by the amine group.

Answer 2

Aniline (C₆H₅NH₂) is an aromatic amine, and its amino group (-NH₂) is an electron-donating group. This makes the ring more reactive towards electrophilic substitution reactions such as nitration, sulphonation, and bromination. However, the amino group also strongly deactivates the ring towards Friedel-Craft reactions (both alkylation and acylation) due to the strong electron-donating nature of the -NH₂ group. 

Therefore, aniline does not undergo Friedel-Craft reactions. It can, however, undergo nitration, sulphonation, and bromination. 

Hence, the correct answer is (C): Friedel-Craft reaction.