What is the major product formed when ${\mathrm{CH}}_2\mathrm{COCH}{2}_{\mathrm{CO}}\mathrm{CH}{2}_{\mathrm{CO}}\mathrm{CH}{2}_{\mathrm{CO}}\mathrm{CH}{2}_{\mathrm{CO}}\mathrm{CH}{2}_{\mathrm{CO}}$ (hexane-2,6-dione) undergoes intramolecular aldol condensation under basic conditions?

• A. $2_{\mathrm{,6}}$-hexanedione
• B. $2_{\mathrm{}}$-cyclohexen-$1_{\mathrm{}}$-one
• C. Cyclohexanone
• D. ${\mathrm{Hexane}}_{\mathrm{2,6}}$-diol

Answer: (B)

Verified step by step guidance

1. Identify the structure of hexane-2,6-dione: it is a six-carbon chain with ketone groups at carbons 2 and 6, i.e., O=C-CH2-CH2-CH2-C=O.
2. Recognize that under basic conditions, an intramolecular aldol condensation can occur when an enolate ion formed at one ketone attacks the other ketone carbonyl within the same molecule, leading to ring formation.
3. Determine which alpha hydrogens are acidic and can form the enolate ion; in this case, the methylene groups adjacent to the ketones (especially at carbon 3 or 5) can form enolates.
4. Draw the enolate ion attacking the carbonyl carbon at the other end of the molecule, resulting in the formation of a new carbon-carbon bond and creating a six-membered ring intermediate (a β-hydroxy ketone).
5. Finally, under the reaction conditions, dehydration occurs (loss of water) to form an α,β-unsaturated ketone, specifically 2-cyclohexen-1-one, which is the major product of the intramolecular aldol condensation.