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Question #44459
The Question
Compound \textbf{P}, (-)-menthyl 2-phenylethanoate, is subjected to free-radical monobromination using 1 equivalent of \ce{NBS} in \ce{CCl4 (l)} under UV irradiation () at 298 K. The reaction yields a mixture of monobrominated products at the benzylic position. What is the stereochemical relationship between these newly formed products, and what is their expected relative molar ratio?
Options
- A.
Enantiomers, ratio
- B.
Diastereomers, ratio
- C.
Diastereomers, ratio
- D.
Enantiomers, ratio
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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
Free Radical Substitution Selectivity|Stereochemical Outcome of Halogenation|Optical Activity and Enantiomers
Why This Question Is Tricky
Common Mistakes
The question tests the 'Chemical Exception' of diastereoselective radical substitution.
Students typically memorize that planar radical intermediates lead to a racemic mixture (1:1 ratio of enantiomers) due to equal probability of attack from both faces.
The hidden variable here is the chiral auxiliary ((-)-menthyl group), which renders the faces of the radical diastereotopic.
This imparts a steric facial bias, causing the bromine transfer to occur at unequal rates from the two faces, yielding diastereomers in a non-1:1 ratio.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Hydrocarbons - Class 11 Part 2 |
| Concept | Free Radical Substitution Selectivity |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |