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Question #44947

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The Question

Consider the compound \textbf{X}, which consists of two aromatic rings connected by an ethylene ( $-\ce{CH2-CH2}-$ ) spacer. Ring A is a phenol ring substituted with a trifluoromethyl group at C3 and the ethylene spacer at C4 (where C1 bears the $-\ce{OH}$ group). Ring B is an $N,N$ -dimethylaniline ring substituted with the ethylene spacer at C2 (where C1 bears the $-\ce{N(CH3)2}$ group). Compound \textbf{X} is treated with 1 equivalent of benzenediazonium chloride ( $\ce{PhN2+ Cl-}$ ) in an aqueous buffer at pH = 9.5 and $0-5^\circ\text{C}$ . Identify the major product of this reaction.

Options

A.
4-(2-(2-(dimethylamino)phenyl)ethyl)-2-(phenyldiazenyl)-5-(trifluoromethyl)phenol
B.
4-(2-(2-(dimethylamino)-5-(phenyldiazenyl)phenyl)ethyl)-3-(trifluoromethyl)phenol
C.
4-(2-(2-(dimethylamino)phenyl)ethyl)-2-(phenyldiazenyl)-3-(trifluoromethyl)phenol
D.
4-(2-(2-(dimethylamino)-3-(phenyldiazenyl)phenyl)ethyl)-3-(trifluoromethyl)phenol

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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

Coupling Reactivity|Azo Coupling Regioselectivity|Inductive Effect Trends

Why This Question Is Tricky

Common Mistakes

This question tests the boundary conditions of electrophilic aromatic substitution regioselectivity.

Students typically memorize the activating group hierarchy ( $-\ce{O^-} > -\ce{NR2}$ ) and default to coupling on the phenoxide ring at pH 9.5.

The trap introduces a strong $-I$ substituent ( $-\ce{CF3}$ ) strategically placed such that it directly bears the positive charge in the Wheland intermediate for the only available attack sites (ortho) on the phenoxide ring.

This massive kinetic destabilization forces the reaction to occur on the seemingly less reactive, but electronically unhindered, para position of the distant $N,N$ -dimethylaniline ring.

It discriminates students who rely on rote rules from those who evaluate the kinetic stability of transition states.

Quick Facts About This Question

Question Information

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