Question

Electrophile NO\(_2^+\) attacks the following compounds. In which cases, NO\(_2\) will be at meta position?

• A. II and IV
• B. I, II and III
• C. II and III
• D. Only I

Hint:

Substituents influence the position of incoming electrophile in aromatic substitution reactions.

Answer 1

The Correct Option is B

The question asks for the identification of compounds where the electrophile NO\(_2^+\) will attack the meta position. To solve this problem, we need to understand the directing effects of substituents on electrophilic aromatic substitution.

Let's analyze each compound:

1. Compound I: CH₃-benzene
   The methyl group (CH₃) is an electron-donating group through hyperconjugation and inductive effect. It is an ortho/para-director, not a meta-director.
2. Compound II: NO₂-benzene
   The nitro group (NO₂) is a strong electron-withdrawing group. It deactivates the benzene ring and directs new electrophilic substituents to the meta position. Therefore, NO\(_2^+\) will attack the meta position.
3. Compound III: NH₃-benzene
   The amino group (NH₃) is an electron-donating group through resonance and is typically an ortho/para director. Yet, in strong acidic conditions due to protonation (forming NH₄⁺), it can become a weak meta-director.
4. Compound IV: O^--benzene
   The phenoxide ion (O^-) is a strong electron-donating group that strongly activates the ring, directing electrophiles to ortho and para positions.

Based on these observations, the nitro group in compound II is a meta director, and due to acidic conditions altering the directing effect, NH₃ in compound III can also direct to the meta position. Hence, the correct answer is: I, II and III.