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Question #44928

Difficulty: 8/10 | 🟢 Free

The Question

Compound \ce{P} ( $C_8H_{11}N$ ) is an aromatic amine that yields 2,6-dimethylphenol upon diazotization followed by heating with water. \ce{P} is subjected to the following two parallel reaction sequences:

Sequence 1: \ce{P} $\xrightarrow{\ce{CH_3I} \text{ (2 eq.)}, \ce{Na_2CO_3}}$ \ce{Q} $\xrightarrow{\text{4-nitrobenzenediazonium chloride, pH 4-5, } 0^\circ C}$ \ce{R}

Sequence 2: \ce{P} $\xrightarrow{\ce{NaNO_2}, \ce{HCl}, 0^\circ C} \xrightarrow{\ce{CuCN}, \ce{KCN}}$ \ce{S} $\xrightarrow{\ce{DIBAL-H}, -78^\circ C} \xrightarrow{\ce{H_2O}}$ \ce{T}

Identify the major products \ce{R} and \ce{T}.

Options

A.
\ce{R} = 4-(4-nitrophenylazo)-2,6-dimethyl- $N,N$ -dimethylaniline; \ce{T} = 2,6-dimethylbenzaldehyde
B.
\ce{R} = No reaction (\ce{Q} is recovered); \ce{T} = 2,6-dimethylbenzaldehyde
C.
\ce{R} = 4-(4-nitrophenylazo)-2,6-dimethyl- $N,N$ -dimethylaniline; \ce{T} = 2,6-dimethylbenzylamine
D.
\ce{R} = No reaction (\ce{Q} is recovered); \ce{T} = 2,6-dimethylbenzoic acid

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Azo Coupling Regioselectivity|Aniline Resonance Pitfalls|Sandmeyer vs Gattermann

Why This Question Is Tricky

Common Mistakes

This problem tests the 'Steric Inhibition of Resonance' (SIR) exception in electrophilic aromatic substitution.

Students often mechanically apply the +M effect of the $-N(CH_3)_2$ group and predict para-azo coupling.

However, the two ortho-methyl groups force the dimethylamino group out of coplanarity with the aromatic ring, shutting down the +M effect and rendering the ring unreactive towards weak electrophiles like diazonium salts.

It also tests the selective reduction of nitriles to aldehydes using DIBAL-H, distinguishing it from complete reduction to amines or hydrolysis to carboxylic acids.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Amines - Class 12
Concept	Azo Coupling Regioselectivity
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free