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Question #45082
The Question
Consider the diastereoselective nucleophilic addition of methylmagnesium bromide () to (2S)-3,3-dimethyl-2-phenylbutanal in anhydrous ether at 195 K. Which prochiral face of the carbonyl group is preferentially attacked, and what is the absolute configuration of the major product formed after aqueous workup?
Options
- A.
Re face attack; Major product is (2S, 3S)-4,4-dimethyl-3-phenylpentan-2-ol
- B.
Si face attack; Major product is (2R, 3S)-4,4-dimethyl-3-phenylpentan-2-ol
- C.
Re face attack; Major product is (2R, 3S)-4,4-dimethyl-3-phenylpentan-2-ol
- D.
Si face attack; Major product is (2S, 3S)-4,4-dimethyl-3-phenylpentan-2-ol
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
Cahn-Ingold-Prelog (CIP) Priority|Nucleophilic Addition Sterics
Why This Question Is Tricky
Common Mistakes
This question tests the 'Nucleophilic Addition Sterics' exception where students blindly conflate CIP priority with steric bulk.
A student relying purely on CIP priority will incorrectly assign the phenyl group (Priority 2) as the 'Large' group over the tert-butyl group (Priority 3).
This lethal error leads to constructing the wrong Felkin-Anh transition state, predicting attack on the opposite prochiral face (Si face), and ultimately selecting the incorrect (2R, 3S) diastereomer.
The problem forces the distinction between stereodescriptor assignment (electronic/atomic number based) and kinetic transition state energy (steric A-value based).
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 |