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Question #44993
The Question
An optically pure sample of -5-methyl-1,5-dihydro-2H-pyrrol-2-one is dissolved in excess containing a catalytic amount of and heated for a prolonged period at . After the system reaches thermodynamic equilibrium, the major tautomer present in the mixture is analyzed. Assuming no back-exchange of isotopes occurs during analysis, which of the following best describes the major isotopologue of this tautomer?
Options
- A.
A racemic mixture of 1,5-dideuterio-5-methyl-1,5-dihydro-2H-pyrrol-2-one
- B.
A racemic mixture of 1,3,5-trideuterio-5-methyl-1,5-dihydro-2H-pyrrol-2-one
- C.
Optically pure -1-deuterio-5-methyl-1,5-dihydro-2H-pyrrol-2-one
- D.
A racemic mixture of 1,3,4,5-tetradeuterio-5-methyl-1,5-dihydro-2H-pyrrol-2-one
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
Nitrogenous Base Keto-Enol Tautomerism|Alpha-Hydrogen Acidity|Enolate Regioselectivity
Why This Question Is Tricky
Common Mistakes
Students typically memorize that alpha-hydrogens to a carbonyl are acidic, and in amides, the N-H is the most acidic.
They will likely identify N-H as the only exchangeable proton (Option C) or perhaps C-3 as an alpha-proton, but C-3 is hybridized (vinylic) in the stable tautomer.
The trap is failing to recognize that the allylic C-5 proton is highly acidic because its removal generates an aromatic pyrrole anion.
Furthermore, they must use resonance to identify that C-3, but not C-4, is part of the delocalized anionic system and thus undergoes exchange.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Biomolecules - Class 12 |
| Concept | Nitrogenous Base Keto-Enol Tautomerism |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |