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Question #44004

Difficulty: 8/10 | 🟢 Free

The Question

An organic compound $P$ , ethyl 2-oxocyclopentane-1-carboxylate, is treated with exactly one equivalent of methylmagnesium bromide ( $\ce{CH3MgBr}$ ) in anhydrous THF at $298\ \text{K}$ . A vigorous evolution of gas $X$ is observed. The resulting reaction mixture is subsequently treated with one equivalent of allyl bromide ( $\ce{CH2=CH-CH2Br}$ ) to yield the major organic product $Y$ . Identify the gas $X$ and the product $Y$ .

Options

A.
$X = \ce{CH4(g)}$ , $Y =$ Ethyl 1-allyl-2-oxocyclopentane-1-carboxylate
B.
$X = \text{No gas evolved}$ , $Y =$ Ethyl 2-hydroxy-2-methylcyclopentane-1-carboxylate
C.
$X = \ce{CH4(g)}$ , $Y =$ Ethyl 2-(allyloxy)cyclopent-1-ene-1-carboxylate
D.
$X = \ce{CH4(g)}$ , $Y =$ Ethyl 3-allyl-2-oxocyclopentane-1-carboxylate

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Grignard Reaction Pathways|Alpha-Hydrogen Acidity|Enolate Regioselectivity

Why This Question Is Tricky

Common Mistakes

The 'Chemical Exception' tested here is the dual nature of Grignard reagents.

While typically taught as potent nucleophiles for carbonyl addition, their extreme basicity dictates that in the presence of acidic protons (like those in 1,3-dicarbonyls), acid-base neutralization is kinetically dominant.

Students often fall into the trap of blindly applying nucleophilic addition (Option B) without evaluating the substrate's $pK_a$ .

Furthermore, the problem tests the regioselectivity of ambident enolate alkylation, where magnesium enolates preferentially undergo C-alkylation with soft electrophiles, trapping students who might guess O-alkylation (Option C) or deprotonation at the less acidic site (Option D).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Grignard Reaction Pathways
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free