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Question #45067

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The Question

An equimolar mixture of phenol and \textit{tert}-butanol is treated with 1.0 equivalent of sodium hydride (\ce{NaH}) in anhydrous THF at 298 K. After the evolution of \ce{H2} gas ceases, 1.0 equivalent of $(R)$ -2-bromobutane is added to the mixture and stirred at 298 K, yielding Compound $\mathbf{P}$ as the major organic product.

In a separate experiment, $(R)$ -2-bromobutane is heated with an excess of potassium \textit{tert}-butoxide in \textit{tert}-butanol at 350 K, yielding Compound $\mathbf{Q}$ as the major organic product.

Which of the following correctly identifies the structures of $\mathbf{P}$ and $\mathbf{Q}$ ?

Options

A.
$\mathbf{P}$ is $(S)$ -2-phenoxybutane; $\mathbf{Q}$ is but-1-ene
B.
$\mathbf{P}$ is $(S)$ -2-phenoxybutane; $\mathbf{Q}$ is \textit{trans}-but-2-ene
C.
$\mathbf{P}$ is $(R)$ -2-phenoxybutane; $\mathbf{Q}$ is but-1-ene
D.
$\mathbf{P}$ is \textit{tert}-butyl \textit{sec}-butyl ether; $\mathbf{Q}$ is \textit{trans}-but-2-ene

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Acidity and Basicity (pKa/pKb)|Williamson Ether Synthesis Constraints

Why This Question Is Tricky

Common Mistakes

This problem tests the student's ability to integrate acidity trends, nucleophilicity vs. basicity, and steric effects in competing reaction pathways.

The 'Hidden Variable' is the selective deprotonation of phenol over tert-butanol due to resonance stabilization of the phenoxide ion.

Students often fall into the trap of assuming Williamson Ether Synthesis always yields an ether (S_N2), failing to recognize that a strong, bulky base like tert-butoxide reacting with a secondary halide forces an E2 mechanism.

Furthermore, the steric hindrance of tert-butoxide dictates anti-Zaitsev (Hofmann) regioselectivity, yielding but-1-ene instead of the more stable but-2-ene.

Finally, the stereochemical inversion from (R) to (S) in the S_N2 pathway ensures rigorous understanding of the transition state.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2
Concept	Acidity and Basicity (pKa/pKb)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free