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Question #44616

Difficulty: 8/10 | 🟢 Free

The Question

An optically pure sample of (2S)-2-bromo-3,3-dimethylbutane is heated in anhydrous methanol at $60^\circ \text{C}$ . The major substitution product $P$ is isolated. Which of the following statements correctly describes the structure of $P$ , its stereochemistry, and the dominant mechanistic pathway?

Options

A.
$P$ is (2R)-2-methoxy-3,3-dimethylbutane, formed via an $S_N2$ mechanism, and is optically active.
B.
$P$ is a racemic mixture of 2-methoxy-3,3-dimethylbutane, formed via an $S_N1$ mechanism without rearrangement.
C.
$P$ is 2-methoxy-2,3-dimethylbutane, formed via an $S_N1$ mechanism with a 1,2-methyl shift, and is optically inactive.
D.
$P$ is 2-methoxy-2,3-dimethylbutane, formed via an $S_N1$ mechanism with a 1,2-methyl shift, and exists as a racemic mixture.

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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

SN2 Stereochemical Inversion|Optical Activity and Enantiomers|Steric Hindrance in SN2

Why This Question Is Tricky

Common Mistakes

Tests the kinetic cutoff between $S_N2$ and $S_N1$ caused by extreme $\beta$ -steric hindrance (neopentyl-like effect).

Students often reflexively apply $S_N2$ inversion to secondary halides.

The trap further exploits stereochemical assumptions: even if a student correctly predicts the $S_N1$ 1,2-methyl shift, they may falsely assume the product retains a chiral center and forms a racemic mixture, failing to realize the rearrangement yields a completely achiral molecule.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Haloalkanes and Haloarenes - Class 12
Concept	SN2 Stereochemical Inversion
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free