When cross aldol condensation is carried out between two different aldehydes, both of which contain α-hydrogen atoms, how many products are formed?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 4
In aldol condensation a molecule with an α-hydrogen loses it to the base and adds to the C=O group of a second molecule. When both aldehydes have α-hydrogens, each can play either part, so a molecule can join with one of its own kind or with the other aldehyde. With ethanal and propanal:
Ethanal + ethanal (self) → but-2-enal: 1 product.
Propanal + propanal (self) → 2-methylpent-2-enal: 1 product.
Ethanal adding to propanal (cross) → pent-2-enal: 1 product.
Propanal adding to ethanal (cross) → 2-methylbut-2-enal: 1 product.
Total: 2 self products + 2 cross products = 4 products.
NCERT (2026-27 edition):
8.4 Chemical Reactions – “(ii) Cross aldol condensation: When aldol condensation is carried out between two different aldehydes and / or ketones, it is called cross aldol condensation. If both of them contain α-hydrogen atoms, it gives a mixture of four products.”