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Question #45061

Difficulty: 8/10 | 🟢 Free

The Question

Consider the following reaction sequence:

(i) $\text{2,3-dimethylbutane} + \ce{Br2} \xrightarrow{h\nu} \textbf{X} \text{ (Major)}$

(ii) $\textbf{X} + \ce{EtO^- Na+} \xrightarrow{\ce{EtOH}, \Delta} \textbf{Q} \text{ (Major)}$

(iii) $\textbf{X} + \ce{t-BuO^- K+} \xrightarrow{\ce{t-BuOH}, \Delta} \textbf{R} \text{ (Major)}$

(iv) $\textbf{R} + \ce{O3} \xrightarrow{\ce{Zn/H2O}} \ce{HCHO} + \textbf{S}$

Let $x$ , $y$ , and $z$ be the number of hyperconjugative $\alpha$ -hydrogens in compounds \textbf{Q}, \textbf{R}, and \textbf{S}, respectively. Determine the value of $(x + y + z)$ .

Options

A.
20
B.
30
C.
26
D.
12

Check Your Answer

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

Hyperconjugation Logic|Haloalkanes and Haloarenes

Why This Question Is Tricky

Common Mistakes

This problem tests the critical exception to Zaitsev's rule driven by steric hindrance in the E2 transition state.

Students often blindly apply hyperconjugation stability to predict the major alkene.

However, when a bulky base like potassium tert-butoxide is used on a sterically hindered alkyl halide (like 2-bromo-2,3-dimethylbutane), the activation energy to abstract the internal tertiary proton becomes prohibitively high due to Van der Waals repulsions.

Consequently, the base abstracts the more accessible primary proton, leading to the kinetically favored Hofmann product.

A secondary trap involves accurately counting $\alpha$ -hydrogens in branched structures, where students frequently misidentify $\beta$ -hydrogens on isopropyl groups as $\alpha$ -hydrogens.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2
Concept	Hyperconjugation Logic
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free