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Question #45058
The Question
Consider the keto-enol tautomerism of 2-methyl-3-oxobutanal in a non-polar solvent () at 298 K. Which of the following represents the thermodynamically most stable enol form present in the equilibrium mixture?
Options
- A.
(3Z)-4-hydroxy-3-methylbut-3-en-2-one
- B.
(2Z)-3-hydroxy-2-methylbut-2-enal
- C.
(3E)-4-hydroxy-3-methylbut-3-en-2-one
- D.
3-hydroxy-2-methylbut-3-enal
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
Hyperconjugation Logic|Tautomerism Conditions
Why This Question Is Tricky
Common Mistakes
This question tests the conflict between Zaitsev-driven stability (hyperconjugation) and Thermodynamic-driven stability (intramolecular H-bonding/chelation).
Students typically quantify the number of hyperconjugative structures to predict alkene stability, leading them to incorrectly select the tetra-substituted enol (Option B) with 6 alpha-hydrogens.
The hidden variable is steric inhibition of resonance: the cis-dimethyl interaction in the highly substituted enol breaks planarity, destroying the chelate ring.
The less substituted enol (Option A) avoids this steric clash, maintaining a strong H-bond and emerging as the thermodynamically dominant species.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2 |
| Concept | Hyperconjugation Logic |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |