NEETChemistryAldehydes and Ketones
When 2,6-octanedione is heated with dilute aqueous NaOH , it undergoes intramolecular aldol condensation to form a mixture of products. Which of the following pairs represents the two possible six-membered cyclic , -unsaturated ketones formed in this reaction?
Options
- A3-Ethylcyclohex-2-en-1-one and 3,4-dimethylcyclohex-2-en-1-one
- B2-Ethylcyclohex-2-en-1-one and 2,3-dimethylcyclohex-2-en-1-one
- C3-Ethylcyclohex-2-en-1-one and 2,3-dimethylcyclohex-2-en-1-one
- D1-Acetyl-2-methylcyclopentene and 3-ethylcyclohex-2-en-1-one
Correct answer
C. 3-Ethylcyclohex-2-en-1-one and 2,3-dimethylcyclohex-2-en-1-one
Step-by-step solution
The reactant is 2,6-octanedione: CH ₃- C (= O )- CH ₂- CH ₂- CH ₂- C (= O )- CH ₂- CH ₃ . It has four enolizable -carbons: C1, C3, C5, and C7. Intramolecular aldol condensation favors the formation of stable five- or six-membered rings. Case 1: Enolate formation at C1 and attack on C6. The C1 carbanion attacks the C6 carbonyl carbon, forming a 6-membered ring. After dehydration, a double bond forms between C1 and C6. The original C2 becomes the ring carbonyl (C1'). The C6 carbon (now C3' of the ring) retains the et