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Question #44838

Difficulty: 8/10 | 🟢 Free

The Question

Compound \textbf{X} (2-bromo-2,3-dimethylbutane) is treated with potassium \textit{tert}-butoxide in \textit{tert}-butanol at 350 K to yield predominantly alkene \textbf{Y}. \textbf{Y} is then reacted with $m$ -CPBA in $CH_2Cl_2$ to form an intermediate \textbf{Z}, which is subsequently treated with methanol in the presence of catalytic $H_2SO_4$ to yield the major product \textbf{W}.

Which of the following correctly identifies the structure of \textbf{W} and the primary mechanistic rationale for the regioselectivity in the formation of \textbf{Y}?

Options

A.
\textbf{W} is 2-methoxy-2,3-dimethylbutan-1-ol; \textbf{Y} is formed via kinetic control due to severe steric strain in the Saytzeff transition state.
B.
\textbf{W} is 3-methoxy-2,3-dimethylbutan-2-ol; \textbf{Y} is formed via thermodynamic control as Saytzeff's rule dictates the most stable alkene.
C.
\textbf{W} is 1-methoxy-2,3-dimethylbutan-2-ol; \textbf{Y} is formed via kinetic control, followed by an $S_N2$ attack of methanol on the less hindered carbon of \textbf{Z}.
D.
\textbf{W} is 3-methoxy-2,3-dimethylbutan-2-ol; \textbf{Y} is formed via an E1 mechanism where the thermodynamic product dominates due to a stable tertiary carbocation.

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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

Activation Energy Trap|E2 Regioselectivity (Saytzeff vs Hoffmann)|E1/E2 Solvent and Base Effects

Why This Question Is Tricky

Common Mistakes

This problem tests the 'Activation Energy Trap' in E2 eliminations and the electronic vs. steric control in epoxide openings.

Students often blindly apply Saytzeff's rule (thermodynamic control) without recognizing that a bulky base ( $t$ -BuOK) reacting with a sterically congested substrate shifts the reaction to kinetic control (Hoffmann product).

Additionally, it traps students who confuse acid-catalyzed epoxide opening (electronic control, attack at more substituted carbon) with base-catalyzed opening (steric control, attack at less substituted carbon).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Kinetics - Class 12
Concept	Activation Energy Trap
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free