Enolate and Related Carbanion Chemistry

A number of other groups such as the nitrile, imine, nitro, sulfoxide, sulfonyl and phosphono, can act as activating groups. These groups may 

In each of the cases where there are two activating groups, the anions are stabilized by delocalization over both activating groups. Different bases are required to generate the anions from these acidic hydrogens. 

Protonation of an enolate anion may take place on the oxygen or on the carbon. This may lead to the exchange of a proton by deuterium. The formation of an enolate and the subsequent regeneration of a ketone may lead to epimerizationand, in the case of a chiral centre, to racemization 

The halogenation of positions adjacent to a carbonyl group takes place via the electrophilic attack of a halonium ion on the enol. Thus the bromination of ketones may be carried out with bromine in acetic acid. 

The carbonyl group is not the only electron-deficient centre at which an enolate carbon may react. Nitrosation using nitrous acid provides a useful method of making C- N bonds. 

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