Question

In the following reaction the reason why meta-nitro product also formed is : 

• A. $-NH_2$ group is highly meta-directive
• B. $-NO_2$ substitution always takes place at meta-position
• C. Formation of anilinium ion
• D. low temperature

Hint:

To obtain only ortho/para products from aniline, you must first "protect" the amino group by acetylation (forming acetanilide) before nitration.

Answer 1

The Correct Option is C

To determine why the meta-nitro product is formed in the given reaction, we need to analyze the role of the substituents and the reaction conditions.

1. The reaction is a nitration of aniline, where a nitro group (-NO_2) is introduced to the benzene ring.
2. Aniline has an amine group (-NH_2), which is generally considered an ortho/para-director and activates the benzene ring towards electrophilic substitution reactions.
3. However, under strongly acidic conditions (like those used in nitration with concentrated nitric and sulfuric acids), the -NH_2 group is protonated to form the anilinium ion (NH_3^+).
4. The formation of the anilinium ion changes the directing effect of the substituent. The protonated amine (NH_3^+) becomes a meta-director and a deactivating group.

Thus, the formation of the anilinium ion is the key reason the meta-nitro product is also formed.

Conclusion: The correct answer is the "Formation of anilinium ion" because this changes the directive nature of the -NH_2 group, leading to meta substitution.