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Question #44407

Difficulty: 8/10 | 🟢 Free

The Question

An optically pure sample of $(R)\text{-2-methoxybutane}$ is heated with excess concentrated $\ce{HI}$ at $373\text{ K}$ . The reaction yields methyl iodide and a chiral alkyl halide $\mathbf{X}$ . Which of the following best describes the stereochemical composition of $\mathbf{X}$ ?

Options

A.
$100\%$ $(S)\text{-2-iodobutane}$
B.
$100\%$ $(R)\text{-2-iodobutane}$
C.
A mixture of $(S)$ and $(R)$ isomers with $(S)\text{-2-iodobutane}$ as the major product
D.
An equimolar (racemic) mixture of $(S)$ and $(R)\text{-2-iodobutane}$

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

Ether Cleavage Patterns|SN2 Stereochemical Inversion|Optical Activity and Enantiomers

Why This Question Is Tricky

Common Mistakes

This question tests the 'Chemical Exception' of idealized $\text{S}_\text{N}2$ mechanisms in secondary substrates under strongly acidic, high-temperature conditions.

Students often rote-memorize that primary and secondary carbons undergo strict $\text{S}_\text{N}2$ ( $100\%$ inversion), while tertiary carbons undergo $\text{S}_\text{N}1$ (racemization).

However, the conversion of secondary alcohols to alkyl halides with hydrogen halides (like $\ce{HI}$ ) proceeds via a borderline mechanism.

The formation of an intimate ion pair allows for partial racemization, contradicting the assumption of $100\%$ Walden inversion.

The trap is Option A (assuming pure $\text{S}_\text{N}2$ ) or Option D (assuming pure $\text{S}_\text{N}1$ due to high temperature).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Alcohols, Phenols, and Ethers - Class 12
Concept	Ether Cleavage Patterns
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free