Which of the following statement is incorrect about aldol condensation
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → The carbonyl compound must possess a β-H atom for undergoing aldol condensation.
In the aldol reaction, dilute alkali removes an α-hydrogen from an aldehyde or ketone to give a carbanion (enolate). This carbanion adds to the C=O carbon of a second molecule, forming a new C–C bond and a β-hydroxy aldehyde (aldol) or β-hydroxy ketone (ketol). On heating, the aldol loses water to give an α,β-unsaturated carbonyl compound (aldol condensation):
\( \ce{2CH3CHO} \xrightarrow{\text{dil. NaOH}} \ce{CH3CH(OH)CH2CHO} \xrightarrow[-\ce{H2O}]{\Delta} \ce{CH3CH=CHCHO} \)
The requirement is an α-hydrogen; a β-hydrogen plays no part.
Option (1) It involves C–C bond formation — True for aldol condensation. The enolate attacks the carbonyl carbon and a new C–C bond is formed.
Option (2) The carbonyl compound must possess an α-H atom — True for aldol condensation. Without an α-hydrogen no enolate can form (e.g. HCHO and \( \ce{C6H5CHO} \) give the Cannizzaro reaction instead).
Option (3) The carbonyl compound must possess a β-H atom — Not true for aldol condensation. The hydrogen removed by the base is the α-hydrogen; no β-hydrogen is needed.
Option (4) α,β-unsaturated carbonyl compound is the product — True for aldol condensation. Dehydration of the aldol gives an α,β-unsaturated aldehyde or ketone, which is the condensation product.
NCERT (2026-27 edition):
Aldol Condensation
