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Question #44617
The Question
Consider the reaction of (2S, 3S)-2,3-dimethyl-2-phenyloxirane with excess methanol in the presence of catalytic at 298 K. Identify the major product(s) and the dominant mechanism governing the stereochemical outcome at the site of nucleophilic attack.
Options
- A.
Only (2S, 3R)-3-methoxy-3-phenylbutan-2-ol, via an -like mechanism with complete inversion.
- B.
A mixture of (2S, 3R)- and (2S, 3S)-3-methoxy-3-phenylbutan-2-ol, via an mechanism.
- C.
Only (2S, 3R)-3-methoxy-2-phenylbutan-2-ol, via an mechanism at the less hindered carbon.
- D.
A racemic mixture of (2S, 3S)- and (2R, 3R)-3-methoxy-3-phenylbutan-2-ol, via an mechanism.
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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
SN2 Stereochemical Inversion|Ether Cleavage Patterns|SN1 Carbocation Rearrangement
Why This Question Is Tricky
Common Mistakes
This question tests the boundary condition of acid-catalyzed epoxide cleavage.
Students are taught that acid-catalyzed opening is 'SN2-like', occurring at the more substituted carbon with inversion of stereochemistry.
The hidden variable here is the exceptional stability of the tertiary benzylic carbocation.
When the intermediate is highly stabilized, the transition state shifts completely to an SN1 mechanism, resulting in a discrete planar carbocation and subsequent epimerization at the reacting center, rather than pure inversion.
Furthermore, it tests IUPAC re-numbering and the retention of stereochemistry at the non-reacting chiral center, distinguishing diastereomeric mixtures from racemic mixtures.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Haloalkanes and Haloarenes - Class 12 |
| Concept | SN2 Stereochemical Inversion |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |