The Knoevenagel condensation involves condensation of aldehydes/ketones with active methylene compounds under base catalysis to yield what?

• A. Acyclic alkanes
• B. α,β-unsaturated compounds
• C. Aldehydes
• D. Ketones

Answer: (B)

The reaction yields α,β-unsaturated carbonyl compounds. In base, an active methylene compound (like a malonate or cyanoacetate) is deprotonated to form a stabilized carbanion, which then adds to the carbonyl of an aldehyde or ketone. After proton transfers and dehydration, a double bond forms between the alpha and beta carbons and remains conjugated to the carbonyl, giving the α,β-unsaturated product (such as an arylidene malonate or related enal/enone). This conjugation is the hallmark of the Knoevenagel product.