Tautomers two constitutional isomers differing in the location of a double bond and a hydrogen. For most ketones, the enol tautomer is much less stable than the keto tautomer. The fraction of enol tautomer is considerably greater for a -diketone because its enol tautomer is stabilized by hydrogen bonding and by conjugation of the carbon-carbon double bond with the second carbonyl group. The interconvesion of the tautomers can be catalyze by either acids or bases. The first step is removal of an -proton and the second step is protonation of the oxygen. The first step is protonation of the oxygen and the second step is removal of an -proton. Ambident nucleophile a nucleophile with two nucleophilic sites. Which nucleophile site will react with an electrophile depends on the electrophile and on the reaction conditions.
