Which of the following is the major enone product formed from the aldol self-condensation of ${\mathrm{CH}}_3\mathrm{COCH}{2}_2\mathrm{CH}{3}_3$ (3-pentanone) under basic conditions, followed by dehydration?

• A. ${\mathrm{CH}}_3\mathrm{COCH}{2}_2\mathrm{CH}{3}_3$ (no reaction, starting material only)
• B. ${\mathrm{CH}}_3\mathrm{COCH}{2}_2=\mathrm{CHCOCH}{2}_2\mathrm{CH}{3}_3$ (4-methyl-3-penten-2-one)
• C. ${\mathrm{CH}}_3\mathrm{COCH}{2}_2=\mathrm{CHCH}{2}_2\mathrm{COCH}{3}_3$ (3-methyl-2-penten-4-one)
• D. ${\mathrm{CH}}_3\mathrm{COCH}{2}_2\mathrm{COCH}{2}_2\mathrm{CH}{3}_3$ (hexane-2,5-dione)

Answer: (B)

Verified step by step guidance

1. Identify the structure of 3-pentanone: it is a ketone with the formula CH3-CO-CH2-CH3, where the carbonyl is at the second carbon of a five-carbon chain.
2. Under basic conditions, the alpha hydrogens adjacent to the carbonyl group are acidic and can be abstracted to form an enolate ion. Determine which alpha hydrogens are most accessible for enolate formation in 3-pentanone.
3. The enolate ion will act as a nucleophile and attack the carbonyl carbon of another 3-pentanone molecule, leading to the formation of a β-hydroxyketone intermediate (aldol addition product). Draw the possible aldol addition products considering the different alpha positions.
4. Under the reaction conditions, the β-hydroxyketone undergoes dehydration (loss of water) to form an α,β-unsaturated ketone (enone). Apply the dehydration step to the aldol addition product to form the conjugated enone.
5. Analyze the possible enone products and determine which is the major product by considering factors such as conjugation, substitution pattern, and stability of the double bond (usually the more substituted and conjugated alkene is favored).