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Question #44614

Difficulty: 8/10 | 🟢 Free

The Question

Consider the reaction of ethyl 5-bromo-4,4-dimethyl-3-oxohexanoate with exactly one equivalent of ethylmagnesium bromide ( $\ce{EtMgBr}$ ) in dry ether at 298 K. The resulting intermediate is then carefully quenched with an excess of $\ce{D_2O}$ . What is the major organic product (P) formed?

Substrate: $\ce{CH3-CH(Br)-C(CH3)2-C(=O)-CH2-CO2Et}$

Options

A.
$\ce{CH3-CH(Br)-C(CH3)2-C(=O)-CHD-CO2Et}$
B.
$\ce{CH3-CH(CH3)-C(Et)(CH3)-C(=O)-CH2-CO2Et}$
C.
$\ce{CH3-CH(Br)-C(CH3)2-C(OD)(Et)-CH2-CO2Et}$
D.
$\ce{CH3-CH(Et)-C(CH3)2-C(=O)-CH2-CO2Et}$

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

SN1 Carbocation Rearrangement|Grignard Reagent Sensitivity|Alpha-Hydrogen Acidity

Why This Question Is Tricky

Common Mistakes

This question tests the 'Acid-Base vs.

Nucleophilic Attack' competitive dominance.

The substrate is deliberately designed as a trap: it features a secondary halide adjacent to a quaternary center (baiting an SN1 carbocation rearrangement with a 1,2-methyl shift) and a ketone (baiting nucleophilic addition).

Students who algorithmically apply Grignard reagents as nucleophiles will fall for the complex structural traps.

The hidden variable is the Bronsted-Lowry basicity of the Grignard reagent.

Because the substrate contains a highly acidic $\beta$ -keto ester moiety, the diffusion-controlled acid-base reaction instantly quenches the Grignard reagent before any nucleophilic attack or rearrangement can occur.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Haloalkanes and Haloarenes - Class 12
Concept	SN1 Carbocation Rearrangement
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free