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Question #44021

Difficulty: 8/10 | 🟢 Free

The Question

Consider the following reaction sequence:

$\ce{Benzene ->[CH_3Cl][anhyd. AlCl_3] A ->[CO, HCl][anhyd. AlCl_3, CuCl] B (Major)}$ $\ce{B ->[(i) [Ag(NH_3)_2]^+, OH^-][(ii) H_3O^+] C ->[(i) CH_3COCl, anhyd. AlCl_3, \Delta][(ii) H_2O] D}$

Identify the major product $\mathbf{D}$ .

Options

A.
3-Acetyl-4-methylbenzoic acid
B.
2-Acetyl-4-methylbenzoic acid
C.
4-Methylbenzoic acid
D.
4-Methylacetophenone

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Friedel-Crafts on Carboxylic Acids|Aniline Resonance Pitfalls|Electrophilic Substitution Control

Why This Question Is Tricky

Common Mistakes

This question tests a classic JEE Advanced trap: the failure of Friedel-Crafts reactions on deactivated rings, specifically focusing on the hidden variable of Lewis acid-base complexation.

Students often mechanically apply directing rules, noting that the $\ce{-COOH}$ group is meta-directing and the $\ce{-CH_3}$ group is ortho/para-directing, and might erroneously predict substitution at the 3-position (ortho to methyl, meta to carboxyl).

However, they fail to account for the fact that the lone pairs on the carboxylic acid coordinate with the $\ce{AlCl_3}$ catalyst.

This not only consumes the catalyst but transforms the $\ce{-COOH}$ group into an exceptionally strong electron-withdrawing complex, completely halting the Friedel-Crafts acylation.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Friedel-Crafts on Carboxylic Acids
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free