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Question #45083
The Question
Consider the reduction of (S)-3-isopropylpent-4-yn-2-one with \ce{NaBH4} in methanol at 298 K. Assuming the reaction proceeds under kinetic control via the Felkin-Anh model, identify the major product formed.
(Note: Assume standard CIP rules for stereochemical assignment)
Options
- A.
(2R, 3S)-3-isopropylpent-4-yn-2-ol
- B.
(2S, 3S)-3-isopropylpent-4-yn-2-ol
- C.
(2R, 3R)-3-isopropylpent-4-yn-2-ol
- D.
(2S, 3R)-3-isopropylpent-4-yn-2-ol
Check Your Answer
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
Cahn-Ingold-Prelog (CIP) Priority|Reduction Selectivity (Hydrides)
Why This Question Is Tricky
Common Mistakes
The question tests the student's ability to distinguish between Cahn-Ingold-Prelog (CIP) priority and actual steric bulk in stereoselective carbonyl reductions.
Students commonly fall into the trap of assigning the 'Large', 'Medium', and 'Small' groups for the Felkin-Anh model based on their CIP priorities.
In this molecule, the ethynyl group (-C#CH) has a higher CIP priority than the isopropyl group (-CH(CH3)2) due to the multiple bonds to carbon, but it is sterically much smaller because of its linear, cylindrical geometry.
Incorrectly assigning the ethynyl group as the 'Large' group leads to the wrong facial approach of the hydride, predicting the (2S, 3S) diastereomer instead of the correct (2R, 3S) major product.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2 |
| Concept | Cahn-Ingold-Prelog (CIP) Priority |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |