Which compound is formed as the major product when two molecules of ${\mathrm{CH}}_3\mathrm{CH}$₂CHO (butanal) undergo aldol condensation in the presence of base?

• A. ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{CH}$₂OH (butanol)
• B. ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{COCH}$₂CHO (4-oxohexanal)
• C. ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{CH}$₂COOH (butanoic acid)
• D. ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{CH}\left(\mathrm{OH}\right)\mathrm{CH}$₂CHO (3-hydroxyhexanal)

Answer: (D)

Verified step by step guidance

1. Identify the reactant: two molecules of butanal (CH\_3CH\_2CHO) are undergoing aldol condensation in the presence of a base.
2. Recall the mechanism of base-catalyzed aldol condensation: the base abstracts an alpha hydrogen from one aldehyde molecule to form an enolate ion.
3. The enolate ion then attacks the carbonyl carbon of a second butanal molecule, forming a new carbon-carbon bond and resulting in a β-hydroxy aldehyde intermediate.
4. Recognize that the initial product before dehydration is a β-hydroxy aldehyde, specifically 3-hydroxyhexanal, formed by the combination of the two butanal molecules.
5. Note that further dehydration of this β-hydroxy aldehyde under the reaction conditions can lead to an α,β-unsaturated aldehyde, but the major product immediately after aldol addition is the β-hydroxy aldehyde (3-hydroxyhexanal).