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Question #44020
The Question
Consider the reaction of diethyl 4-(3-bromopropyl)heptanedioate with excess \ce{NaOEt} in ethanol at reflux, followed by mild acidic workup. Identify the major organic product formed under thermodynamic control.
Options
- A.
Ethyl 2-oxobicyclo[3.3.1]nonane-1-carboxylate
- B.
Ethyl 3-(3-ethoxy-3-oxopropyl)cyclohexane-1-carboxylate
- C.
Ethyl 2-oxobicyclo[4.2.1]nonane-1-carboxylate
- D.
Ethyl 2-oxobicyclo[2.2.2]octane-1-carboxylate
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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
Enolate Regioselectivity|Esterification Reversibility
Why This Question Is Tricky
Common Mistakes
The question tests the kinetic vs thermodynamic control of intramolecular reactions.
Students often fall into the trap of assuming the first possible irreversible step (direct alkylation of the ester enolate) dictates the major product.
However, they fail to account for the reversible Dieckmann condensation acting as a thermodynamic funnel.
Because the Dieckmann condensation generates a much more acidic -keto ester, complete deprotonation of this intermediate drives the equilibrium forward.
Subsequent irreversible alkylation of this specific, highly stable enolate yields the bicyclic product.
Ignoring the relative pKa values and the reversibility of the acyl substitution leads to the incorrect monocyclic distractor.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Aldehydes, Ketones, and Carboxylic Acids - Class 12 |
| Concept | Enolate Regioselectivity |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |