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Question #44018

Difficulty: 8/10 | 🟢 Free

The Question

Consider the reaction of 2-ethyl-5-methyl-3-oxohexanenitrile with 1.05 equivalents of Lithium diisopropylamide (LDA) in anhydrous THF at $-78^\circ\text{C}$ for 1 hour. To this mixture, 1.1 equivalents of methyl iodide (\ce{CH3I}) is added, and the reaction is allowed to warm to room temperature. Identify the major organic product formed.

Options

A.
2-ethyl-2,5-dimethyl-3-oxohexanenitrile
B.
2-ethyl-4,5-dimethyl-3-oxohexanenitrile
C.
2-ethyl-3-methoxy-5-methylhex-2-enenitrile
D.
4-ethyl-2,5-dimethyl-3-oxohexanenitrile

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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

Enolate Regioselectivity|Inductive Effect Trends

Why This Question Is Tricky

Common Mistakes

This question tests the boundary conditions of the 'kinetic vs. thermodynamic enolate' heuristic.

Students are taught that bulky bases (LDA) at low temperatures ( $-78^\circ\text{C}$ ) abstract the least hindered proton to form the kinetic enolate.

However, this 'steric-only' model fails when a strong electron-withdrawing group (like -CN) is present at the more hindered position.

The EWG drastically lowers the pKa of the hindered proton.

This massive thermodynamic driving force lowers the activation energy for deprotonation so much that the sterically hindered proton is abstracted kinetically as well.

The trap is choosing the less hindered C4 alkylation product by blindly applying the LDA/ $-78^\circ\text{C}$ rule without considering the overriding electronic effect.

Quick Facts About This Question

Question Information

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