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Question #43954

Difficulty: 8/10 | 🟢 Free

The Question

An acyclic compound $\textbf{X}$ is 4-(benzylamino)butanal. It is subjected to two different reaction conditions: \begin{itemize} \item \textbf{Reaction 1:} $\textbf{X}$ is treated with 1 equivalent of \ce{NaCN} in an aqueous buffer at pH = 9.5 at 298 K. The major product isolated is $\textbf{P}$ . \item \textbf{Reaction 2:} $\textbf{X}$ is treated with 1 equivalent of \ce{NaCN} in an aqueous buffer at pH = 4.5 at 298 K. The major product isolated is $\textbf{Q}$ . \end{itemize} Identify the major products $\textbf{P}$ and $\textbf{Q}$ .

Options

A.
$\textbf{P}$ = 5-(benzylamino)-2-hydroxypentanenitrile; $\textbf{Q}$ = 1-benzylpyrrolidine-2-carbonitrile
B.
$\textbf{P}$ = 1-benzylpyrrolidine-2-carbonitrile; $\textbf{Q}$ = 5-(benzylamino)-2-hydroxypentanenitrile
C.
$\textbf{P}$ = 5-(benzylamino)-2-hydroxypentanenitrile; $\textbf{Q}$ = 1-benzylpiperidine-2-carbonitrile
D.
$\textbf{P}$ = 5-(benzylamino)-2-hydroxypentanenitrile; $\textbf{Q}$ = 5-(benzylamino)-2-hydroxypentanenitrile

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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

Schiff Base pH Dependence|Cyanohydrin Stereochemistry

Why This Question Is Tricky

Common Mistakes

The question tests the pH-dependent speciation and reactivity of bifunctional molecules (amino-aldehydes) in the presence of cyanide.

At basic pH (9.5), cyanohydrin formation is favored because the abundant cyanide attacks the open-chain aldehyde, while the cyclic hemiaminal cannot dehydrate without acid.

At acidic pH (4.5), the cyclic hemiaminal undergoes acid-catalyzed dehydration to a highly electrophilic cyclic iminium ion.

Despite the low concentration of free cyanide, the iminium ion is reactive enough to undergo nucleophilic attack, yielding the cyclic alpha-aminonitrile (Strecker-type product).

The trap is assuming that the same product forms regardless of pH, or miscounting the carbon chain to form a piperidine ring.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Schiff Base pH Dependence
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free