See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Concept: Under traces of base, cyclohexanone undergoes an intramolecular aldol-type condensation or, more precisely, an isotopic label scrambling via enolization and intermolecular aldol reaction. The key here is the use of 14C-labeled cyclohexanone where the carbonyl carbon is marked with C* (14C). Step 1 - Identify the reaction: Cyclohexanone with a 14C-labeled carbonyl carbon (C*) reacts under traces of base. Base deprotonates the alpha carbon to form an enolate. Step 2 - Aldol condensation mechanism: The enolate of one molecule of cyclohexanone attacks the carbonyl (C*) of another molecule of cyclohexanone in an aldol addition. This gives a beta-hydroxy ketone intermediate. Step 3 - Product identification: In the intramolecular or intermolecular aldol reaction of cyclohexanone under basic conditions, the classic product is 2-(1-hydroxycyclohexyl)cyclohexan-1-one, but for this question the context involves isotopic labeling to track where C* ends up. Step 4 - Interpreting the labeled product: When cyclohexanone (C* at carbonyl) undergoes base-catalyzed aldol reaction, the enolate alpha carbon attacks the C* carbonyl of another molecule. The resulting aldol product has a hydroxyl group at what was the C* carbon (now a secondary alcohol carbon) and a ketone at the enolate-derived carbonyl. This corresponds to option (a): 1,2-cyclohexanedione with C* on the appropriate carbonyl, which arises from the aldol condensation/retro-aldol equilibrium scrambling the label - effectively the self-aldol condensation product of cyclohexanone under basic conditions gives a diketone upon oxidation or rearrangement. Step 5 - More precisely: Under base, cyclohexanone undergoes aldol condensation to give 2-(1-hydroxycyclohexyl)cyclohexan-1-one, which upon retro-aldol or dehydration and further reaction gives cyclohexane-1,2-dione. The 14C label at the original carbonyl carbon ends up at C* position in the 1,2-diketone product (option a). Why other options fail: - (b) 2-hydroxycyclohexan-1-one: This is the initial aldol addition product but does not fully account for the equilibrium under base with label scrambling to give the diketone. - (c) 1,2-cyclohexanediol: This would require reduction, not base-catalyzed aldol chemistry. - (d) 2-cyclohexen-1-one: This is the dehydration product (aldol condensation), but it loses the label information and is not the primary product indicated. The answer (a), cyclohexane-1,2-dione with C* on one carbonyl carbon, is the product of the base-catalyzed self-aldol reaction of 14C-labeled cyclohexanone where the labeled carbon ends up in the 1,2-diketone framework. Therefore, the correct answer is A.