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Question #43967
The Question
An equimolar mixture of \ce{tert-butyl 5,5-dimethyl-4-oxohexanoate} and benzaldehyde is treated with an excess of aqueous \ce{NaOH} at for an extended period. The reaction mixture is then subjected to careful acidic workup. Which of the following is the major aliphatic product isolated?
Options
- A.
\ce{3-benzylidene-5,5-dimethyl-4-oxohexanoic acid}
- B.
\ce{tert-butyl 3-benzylidene-5,5-dimethyl-4-oxohexanoate}
- C.
\ce{5,5-dimethyl-4-oxohexanoic acid}
- D.
\ce{2-benzylidene-5,5-dimethyl-4-oxohexanoic acid}
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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
Aldol Condensation Directionality|Esterification Steric Hindrance|Esterification Reversibility
Why This Question Is Tricky
Common Mistakes
The problem tests the kinetic vs. thermodynamic competition between Aldol condensation and ester saponification in sterically hindered systems.
Students often default to 'Aldol = Base' and assume tert-butyl esters are completely inert to basic hydrolysis.
However, the S_N2-like attack of hydroxide on the ester is kinetically more favorable than the highly congested Aldol transition state caused by the adjacent tert-butyl ketone.
Once saponification occurs, the resulting carboxylate anion suppresses enolate formation due to the thermodynamic penalty of forming a dianion.
Furthermore, the electrophile (benzaldehyde) is consumed via the Cannizzaro reaction, ensuring a complete competitive path failure for the Aldol condensation.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Aldehydes, Ketones, and Carboxylic Acids - Class 12 |
| Concept | Aldol Condensation Directionality |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |