Before You Begin

Question #44633

Difficulty: 8/10 | 🟢 Free

The Question

An optically active alkyl halide, (2 $S$ , 3 $R$ )-2-bromo-3-methylpentane, is subjected to two different sets of reaction conditions:

Condition I: Treatment with 1.0 equivalent of \ce{NaI} in anhydrous acetone at 298 K yields major product P. Condition II: Treatment with 1.0 equivalent of \ce{NaOMe} in methanol at 330 K yields major product Q.

Which of the following correctly identifies the stereochemistry of P and Q?

Options

A.
P is (2 $R$ , 3 $R$ )-2-iodo-3-methylpentane; Q is ( $E$ )-3-methylpent-2-ene
B.
P is (2 $R$ , 3 $R$ )-2-iodo-3-methylpentane; Q is ( $Z$ )-3-methylpent-2-ene
C.
P is (2 $S$ , 3 $R$ )-2-iodo-3-methylpentane; Q is ( $E$ )-3-methylpent-2-ene
D.
P is (2 $S$ , 3 $R$ )-2-iodo-3-methylpentane; Q is ( $Z$ )-3-methylpent-2-ene

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

Finkelstein and Swarts Exchange|E1/E2 Solvent and Base Effects|SN2 Stereochemical Inversion

Why This Question Is Tricky

Common Mistakes

This question tests the competition between S $_\text{N}$ 2 and E2 pathways dictated by solvent and reagent choices, alongside rigorous stereochemical analysis.

The Finkelstein condition (polar aprotic solvent) isolates the S $_\text{N}$ 2 pathway, testing the student's ability to invert only the reacting chiral center.

The E2 condition (strong base, protic solvent, heat) tests the anti-periplanar requirement on a chiral substrate.

Students often misapply the Newman projection rotations, incorrectly predicting the ( $Z$ )-alkene.

The hidden variable is the pre-existing anti-periplanar geometry in the staggered conformation, which directly dictates the formation of the ( $E$ )-isomer.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Haloalkanes and Haloarenes - Class 12
Concept	Finkelstein and Swarts Exchange
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free