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Question #44495

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The Question

Consider the following two independent reactions performed on (Z)-3-methylpent-2-ene (Compound X):\Reaction 1: X is treated with $\ce{BH3 \cdot THF}$ followed by alkaline $\ce{H2O2}$ to yield the major product Y.\Reaction 2: X is treated with $\ce{Br2}$ in $\ce{CCl4}$ to yield the major product Z.\Which of the following correctly describes the stereochemistry of the major products Y and Z?

Options

A.
Y is a racemic mixture of (2S,3R) and (2R,3S)-3-methylpentan-2-ol; Z is a racemic mixture of (2S,3S) and (2R,3R)-2,3-dibromo-3-methylpentane.
B.
Y is an achiral compound (3-methylpentan-3-ol); Z is a racemic mixture of (2S,3R) and (2R,3S)-2,3-dibromo-3-methylpentane.
C.
Y is a racemic mixture of (2S,3S) and (2R,3R)-3-methylpentan-2-ol; Z is a racemic mixture of (2S,3R) and (2R,3S)-2,3-dibromo-3-methylpentane.
D.
Y is a racemic mixture of (2S,3R) and (2R,3S)-3-methylpentan-2-ol; Z is a meso compound.

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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

Hydroboration-Oxidation Logic|Stereochemical Outcome of Halogenation

Why This Question Is Tricky

Common Mistakes

The problem tests the student's ability to differentiate between the concerted syn-addition mechanism of hydroboration and the anti-addition bridged-ion mechanism of halogenation.

A common trap is applying 'Markovnikov-like' regioselectivity to hydroboration, which incorrectly yields an achiral product (3-methylpentan-3-ol).

Furthermore, students often confuse the stereochemical outcomes (erythro vs threo) when transitioning between syn and anti additions on a (Z)-alkene.

The hidden variable is the precise R/S configuration mapping from the erythro/threo relative stereochemistry, requiring rigorous spatial visualization.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Hydrocarbons - Class 11 Part 2
Concept	Hydroboration-Oxidation Logic
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free