Question

What is the product formed when chlorobenzene undergoes nitration with concentrated $HNO_3$ and $H_2SO_4$?

• A. Nitrobenzene
• B. 1,3-Dinitrobenzene
• C. o- and p-Nitrochlorobenzene
• D. Chlorobenzene sulfonic acid

Hint:

Important Directing Effects in Aromatic Substitution: Halogens ($-Cl$, $-Br$, $-I$) are ortho-para directing but deactivating. Examples: Chlorobenzene nitration $\rightarrow$ o- and p-nitrochlorobenzene.

Answer 1

The Correct Option is C

Concept: Nitration of aromatic compounds is an example of an electrophilic aromatic substitution reaction. In this reaction, a nitro group ($-NO_2$) is introduced into the benzene ring. The nitrating mixture consists of: \[ \text{Conc. } HNO_3 + \text{Conc. } H_2SO_4 \] Sulfuric acid acts as a catalyst and helps generate the nitronium ion ($NO_2^+$), which is the active electrophile. \[ HNO_3 + H_2SO_4 \rightarrow NO_2^+ + HSO_4^- + H_2O \]

Step 1: Understand the directing effect of chlorine. Chlorine is an ortho-para directing group. Although it is slightly deactivating due to its electron-withdrawing inductive effect ($-I$), it donates electron density to the ring through resonance ($+R$ effect). Therefore, substitution occurs mainly at:
• Ortho position
• Para position

Step 2: Formation of nitration products. When chlorobenzene reacts with the nitrating mixture, the nitro group enters mainly at the ortho and para positions relative to chlorine. The products formed are: \[ o\text{-Nitrochlorobenzene} \quad \text{and} \quad p\text{-Nitrochlorobenzene} \]

Step 3: Reason for two products. Because both ortho and para positions are activated by the chlorine substituent, a mixture of ortho and para substituted products is formed. Thus, the nitration of chlorobenzene produces o- and p-nitrochlorobenzene.