Question

Chlorobenzene is formed by the reaction between benzene and chlorine in presence of \(\text{AlCl}_{3}\). Which of the following species actually attacks the benzene ring in this reaction?

• A. \(\text{Cl}^{-}\)
• B. \(\text{Cl}_{2}\)
• C. \(\text{Cl}^{+}\)
• D. \(\text{AlCl}_{4}^{-}\)

Hint:

The Lewis acid generates a chloronium ion, which is the electrophile.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Chlorination of benzene is electrophilic substitution, so the species attacking the ring must be an electrophile.

Step 2: Generation of the electrophile
\(\text{AlCl}_{3}\) is a Lewis acid and takes a chloride from \(\text{Cl}_{2}\): \(\text{Cl}_{2}+\text{AlCl}_{3}\rightarrow\text{Cl}^{+}+\text{AlCl}_{4}^{-}\).

Step 3: Attack on the ring
The electron-poor \(\text{Cl}^{+}\) attacks the pi electrons of benzene to give the arenium ion. Loss of a proton then restores the aromatic ring.

Final Answer:
The attacking species is \(\text{Cl}^{+}\). \[ \boxed{\text{(C) }\text{Cl}^{+}} \]