The compound shown is warmed with dilute aqueous sodium hydroxide. Loss of water gives which major organic product?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: B

The compound is 3-hydroxybutanal, a beta-hydroxy aldehyde. Hydroxide forms the enolate by removing the acidic alpha-hydrogen, and the enolate expels hydroxide from the beta-carbon (E1cB). The conjugated product is the more stable trans-but-2-enal (crotonaldehyde), not the non-conjugated but-3-enal.

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