GAS-PHASE REACTIVITY OF AMBIDENT THIO-ENOLATE AND OXIMATE ANIONS

The gas-phase chemical behaviour of ambident thio-enolate anions from thioacetaldehyde and oximate anions from acetaldoxime and acetone oxim e has been studied using the method of Fourier-transform ion cyclotron resonance mass spectrometry. It appears that the thio-enolate anions, generated by an efficient base-induced E2 elimination of ethene from ethyl vinyl sulfide, exhibit a strong preference for addition via the sulfur rather than via the carbon nucleophilic center in the reactions with a series of unsaturated polyfluorocarbon compounds. This preferr ed addition via the sulfur nucleophilic center is considered to be pro moted both by specific frontier orbital and by electrostatic interacti ons between the reactants. Further, acetaldoxime and acetone oximate a nions exclusively react via the oxygen nucleophilic center with the se ries of unsaturated polyfluorocarbon compounds. Electrostatic interact ions are held responsible for the reaction selectivity of the oximate anions. This is in contrast with the corresponding enolate anions, for which it is considered that the previously studied ambident chemical behaviour is governed by specific frontier orbital interactions.