What is aldol condensation? Explain using acetaldehyde.

Aldol condensation is a reaction in which aldehydes or ketones containing an α-hydrogen combine to form a β-hydroxy aldehyde or ketone, which may further dehydrate to give an α,β-unsaturated carbonyl compound.

Using acetaldehyde:

2CH₃CHO ⟶ CH₃CH(OH)CH₂CHO ⟶ CH₃CH=CHCHO + H₂O

In the presence of a dilute base, two molecules of acetaldehyde form 3-hydroxybutanal (aldol). On heating, it loses water to produce crotonaldehyde (but-2-enal).

Quick Fact: The term "aldol" comes from aldehyde + alcohol, reflecting the functional groups present in the product.