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Question #44512

Difficulty: 8/10 | 🟢 Free

The Question

Consider the hydration of \ce{3,3-dimethylbut-1-yne} using aqueous \ce{HgSO4} and \ce{H2SO4} at $298\text{ K}$ . For standard terminal alkynes, this reaction exclusively yields methyl ketones. However, for this substrate, the transition state for the standard pathway is severely destabilized by 1,3-diaxial-like steric interactions with the bulky $t$ -butyl group. This kinetic bottleneck shifts the reaction flux, producing a significant yield of an anomalous carbonyl product, $\mathbf{P}$ , via an alternative hydration pathway. What is the total number of $\alpha$ -hydrogens in $\mathbf{P}$ ?

Options

A.
2
B.
3
C.
0
D.
1

Check Your Answer

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

Alkyne Hydration Tautomerization|Nucleophilic Addition Sterics|Reaction Intermediates Stability

Why This Question Is Tricky

Common Mistakes

Tests the student's ability to recognize when extreme steric hindrance overrides standard electronic effects (Markovnikov's rule).

Students often blindly apply the 'terminal alkynes yield methyl ketones' rule, failing to account for the transition state destabilization caused by the bulky t-butyl group, which redirects the nucleophile to the terminal carbon.

It also traps students who might incorrectly propose a carbocation rearrangement (1,2-methyl shift, leading to 1 alpha-hydrogen), forgetting that the reaction proceeds via a bridged mercurinium intermediate, not a free vinyl cation.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Hydrocarbons - Class 11 Part 2
Concept	Alkyne Hydration Tautomerization
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free