Compound	pKa	Structural Note
Ethyl acetate (ester α-C–H)	25	One carbonyl stabilizes the enolate by resonance
Acetone (ketone α-C–H)	20	One carbonyl stabilizes the enolate by resonance; ketones are somewhat more acidic than esters at the α-position
Diethyl malonate (1,3-diester α-C–H)	~13	Two carbonyls both stabilize the same enolate — resonance delocalizes the negative charge onto two separate carbonyl oxygens
Acetylacetone (1,3-diketone α-C–H)	~9	Two carbonyls, same doubly-stabilized effect, and ketone carbonyls stabilize slightly better than ester carbonyls

Why α-carbons are acidic at all: deprotonating a C–H adjacent to a carbonyl generates an enolate, whose negative charge is resonance-delocalized onto the carbonyl oxygen rather than sitting on carbon alone (Chapter 14). This is the same stability principle as carboxylate and phenoxide — resonance delocalization of the conjugate base — applied to a carbanion instead of an alkoxide.

Why 1,3-dicarbonyls are dramatically more acidic: with two carbonyls flanking the same C–H, the single resulting enolate can delocalize onto either carbonyl oxygen, effectively doubling the resonance stabilization. This is why diethyl malonate and acetylacetone are common starting materials for enolate alkylation chemistry (Chapter 14) — their α-protons are acidic enough to be removed by moderate bases like alkoxide, rather than requiring the very strong bases needed for a simple ketone or ester.

---