Acidity of a-hydrogen atoms enolate ion formation

Bases can abstract a-hydrogen atoms from carbonyl compounds to form enolate ions. 

Carbonyl compounds are more acidic than, for example, alkanes because the anion is stabilised by resonance (see Section 4.3.1). 

3-Diketones (or (3-diketones) are therefore more acidic than water (which has a pA a value of 16), as the enolate ion is stabilised by resonance over both carbonyl groups. 

Nucleophiles, like enolate ions, that 8.4.4 RSSCtivity Of HOlStSS 

Reaction of methyl ketones (RCOCH3) with excess hydroxide and chlorine, bromine or iodine leads to a carboxylic acid (RCO2H) together with CHX3 in a haloform reaction. The use of iodine gives CHI3 (iodoform or triiodomethane), which is the basis of a functional group test for methyl ketones. 

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During the discussion of base-catalyzed enol formation in Section 22.1, we said that carbonyl compounds can act as weak protic acids. That is, a strong base can abstract an acidic a hydrogen atom from a carbonyl compound to yield an enolate ion. 

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