The Aldol Condensation is a crucial C-C bond-forming reaction.

• Requirement: An aldehyde or ketone must possess at least one $\alpha$-hydrogen atom.
• Mechanism: A base (like dilute $NaOH$) abstracts the acidic $\alpha$-hydrogen to form a resonance-stabilized enolate ion. This ion then acts as a nucleophile, attacking the carbonyl carbon of another molecule.
• Product: A $\beta$-hydroxy aldehyde (Aldol) or $\beta$-hydroxy ketone, which often dehydrates on heating to form an $\alpha ,\beta$-unsaturated carbonyl compound.