In the first step of aldol condensation, what does the base do to the alpha-hydrogen?

• A. It oxidizes it
• B. It protonates it
• C. It deprotonates it
• D. It reduces it

Answer: (C)

In the first step of aldol condensation, the base plays a crucial role by deprotonating the alpha-hydrogen of a carbonyl compound, such as an aldehyde or ketone. This results in the formation of an enolate ion, which is a resonance-stabilized anion. The deprotonation occurs because the alpha-hydrogen is relatively acidic due to the electron-withdrawing nature of the carbonyl group, making it easier for a base to remove it.

Once the enolate ion is formed, it can act as a nucleophile and attack the electrophilic carbonyl carbon of another molecule, leading to the formation of a β-hydroxy carbonyl compound. Subsequently, this compound can undergo dehydration to produce an α,β-unsaturated carbonyl compound.

The other answer choices do not accurately describe the action of the base in the context of aldol condensation. For example, there is no oxidation, addition of protons, or reduction occurring at this initial stage of the reaction. Therefore, the process of deprotonating the alpha-hydrogen by the base is the critical first step that initiates the aldol condensation pathway.