Understanding Nitration of Benzene Derivatives

The question concerns the mono-nitration of substituted benzene rings using a mixture of concentrated nitric acid (HNO$_3$) and sulfuric acid (H$_2$SO$_4$). This reaction proceeds via Electrophilic Aromatic Substitution (EAS). The key factor determining the product distribution is the directing effect of the substituent already attached to the benzene ring.

Substituent Effects on Nitration Regioselectivity

Substituents influence the position of electrophilic attack:

• Nitrobenzene (Option 3): Contains the -NO$_2$ group. This is a strongly deactivating group and a meta director. It guides the incoming nitro group predominantly to the meta position relative to itself.
• Benzoic Acid (Option 4): Contains the -COOH group. This is also a deactivating group and a meta director, favoring substitution at the meta position.
• Aniline (Option 1): Contains the -NH$_2$ group. While typically activating and ortho/para directing, in the highly acidic environment of the nitrating mixture, the -NH$_2$ group gets protonated to -NH$_3^+$. This protonated form is deactivating and acts as a meta director, favoring meta-substitution.
• Phenol (Option 2): Contains the -OH group. This is a strongly activating group and an ortho/para director. It directs the incoming nitro group primarily to the ortho and para positions. Consequently, the meta-isomer is not the major product.

Identifying the Compound NOT Yielding a Meta-Major Product

The question asks to identify the compound for which the meta-isomer is NOT the major product after mono-nitration.

Based on the directing effects:

• Aniline (Option 1), Nitrobenzene (Option 3), and Benzoic Acid (Option 4) all predominantly yield the meta-isomer under these reaction conditions.
• Phenol (Option 2) directs the substitution to the ortho and para positions.

Option C is identified as the answer.