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Question #44638

Difficulty: 8/10 | 🟢 Free

The Question

Consider the enantiomerically pure compound $\mathbf{X}$ , $(R)$ -2-hydroxy-2-phenylpropanenitrile.

Experiment 1: $\mathbf{X}$ is treated with 1 equivalent of $\ce{CH3MgBr}$ in dry ether at 298 K, followed by mild aqueous workup to yield major product $\mathbf{Y}$ .

Experiment 2: $\mathbf{X}$ is treated with excess $\ce{LiAlH4}$ in dry ether at 298 K, followed by aqueous workup to yield major product $\mathbf{Z}$ .

Identify the major products $\mathbf{Y}$ and $\mathbf{Z}$ .

Options

A.
$\mathbf{Y}$ = Acetophenone; $\mathbf{Z}$ = $(R)$ -1-amino-2-phenylpropan-2-ol
B.
$\mathbf{Y}$ = $(R)$ -3-hydroxy-3-phenylbutan-2-one; $\mathbf{Z}$ = $(R)$ -1-amino-2-phenylpropan-2-ol
C.
$\mathbf{Y}$ = Acetophenone; $\mathbf{Z}$ = 1-phenylethan-1-ol
D.
$\mathbf{Y}$ = $(R)$ -3-hydroxy-3-phenylbutan-2-one; $\mathbf{Z}$ = 1-phenylethan-1-ol

Check Your Answer

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

Grignard Reagent Sensitivity|Reduction Selectivity (Hydrides)|Cyanohydrin Stereochemistry

Why This Question Is Tricky

Common Mistakes

This problem tests the hierarchy of Grignard reactivity (acid-base > nucleophilic addition) and the specific instability of cyanohydrin alkoxides.

Students often mechanically add the Grignard to the nitrile, forgetting the protic -OH group.

Furthermore, they miss that deprotonation of a cyanohydrin by a Grignard reagent leads to retro-cyanohydrin collapse (yielding a ketone), destroying the stereocenter.

Conversely, LiAlH4 coordinates the oxygen strongly, preventing collapse and allowing the reduction of the nitrile to a primary amine, preserving the chiral center.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Haloalkanes and Haloarenes - Class 12
Concept	Grignard Reagent Sensitivity
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free