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Question #45075

Difficulty: 8/10 | 🟢 Free

The Question

Consider the hydrocarbon \textbf{X}, 3-methyl-1-butene. It is subjected to three distinct reaction conditions to yield major products \textbf{P}, \textbf{Q}, and \textbf{R}:

I. $\ce{X + HBr ->[(PhCOO)2, h\nu, 298 K]}$ \textbf{P} II. $\ce{X + NBS ->[CCl4, h\nu, 353 K]}$ \textbf{Q} III. $\ce{X + HBr ->[Dark, no peroxides, 298 K]}$ \textbf{R}

Identify the major products \textbf{P}, \textbf{Q}, and \textbf{R}.

Options

A.
\textbf{P} = 1-bromo-3-methylbutane; \textbf{Q} = 1-bromo-3-methyl-2-butene; \textbf{R} = 2-bromo-2-methylbutane
B.
\textbf{P} = 1-bromo-2-methylbutane; \textbf{Q} = 3-bromo-3-methyl-1-butene; \textbf{R} = 2-bromo-2-methylbutane
C.
\textbf{P} = 1-bromo-3-methylbutane; \textbf{Q} = 3-bromo-3-methyl-1-butene; \textbf{R} = 2-bromo-3-methylbutane
D.
\textbf{P} = 2-bromo-2-methylbutane; \textbf{Q} = 1-bromo-3-methyl-2-butene; \textbf{R} = 1-bromo-3-methylbutane

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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

Electrophile vs Nucleophile|Bond Cleavage Energetics|Free Radical Substitution Selectivity

Why This Question Is Tricky

Common Mistakes

This problem tests the fundamental divergence between polar and radical potential energy surfaces.

A common cognitive trap is erroneously applying carbocation rearrangement rules (1,2-shifts) to free radical intermediates, failing to realize that radical rearrangements have prohibitively high activation energies.

Furthermore, in allylic bromination (NBS), students frequently fall for the trap of placing the bromine atom at the site of the initial radical (tertiary carbon), ignoring that the delocalized allylic radical will react at the less sterically hindered position to yield the thermodynamically more stable, highly substituted alkene (trisubstituted vs. monosubstituted).

Quick Facts About This Question

Question Information

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