How many aldol condensation products can be obtained when two aldehydes, both with \(\alpha \)-hydrogen atoms undergo reaction?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 4
An aldol condensation needs an aldehyde or ketone with an α-hydrogen: dilute alkali removes it to give a carbanion (enolate), which adds to the C=O group of another molecule. When two different aldehydes are used, it is a cross aldol condensation. If both have α-hydrogen atoms, each can act as the carbanion and each as the carbonyl partner, so there are 2 × 2 = four products: two self-condensation products and two cross products.
For example, ethanal + propanal gives
but-2-enal (ethanal + ethanal, self);
2-methylpent-2-enal (propanal + propanal, self);
pent-2-enal (carbanion of ethanal + propanal, cross);
2-methylbut-2-enal (carbanion of propanal + ethanal, cross).
NCERT (2026-27 edition):
Cross Aldol Condensation
