Answer
🧪 Aldol Condensation: Step-wise Mechanism of Butanal
🔹 Step 1: Formation of Enolate Ion
A strong base such as OH⁻ abstracts an acidic α-hydrogen from butanal, forming an enolate ion stabilized by resonance.
CH₃–CH₂–CH⁻–CHO ⇌ CH₃–CH₂–C⁻=CH–O⁻
🔹 Step 2: Nucleophilic Attack on a Second Butanal Molecule
The enolate ion acts as a nucleophile and attacks the carbonyl carbon of another butanal molecule, forming a new C–C bond.
CH₃–CH₂–CH⁻–CHO + CH₃–CH₂–CH₂–CHO → CH₃–CH₂–CH(OH)–CH₂–CH₂–CHO
🔹 Step 3: Protonation
The alkoxide oxygen gets protonated from the solvent or water, forming a stable β-hydroxy aldehyde (aldol product).
CH₃–CH₂–CH(OH)–CH₂–CH₂–CHO
🔹 Step 4: Dehydration (Elimination of Water)
Upon heating, the β-hydroxy aldehyde undergoes elimination (E1cb mechanism), forming an α,β-unsaturated aldehyde.
CH₃–CH₂–CH=CH–CH₂–CHO + H₂O
✅ Final Product: CH₃–CH₂–CH=CH–CH₂–CHO (α,β-unsaturated aldehyde)