Enol and Enethioenol Occurrence for Some Ketones and Thioketones. Mass Spectrometry and Theoretical Calculations

The mass spectra of ketones can provide valuable information in regard to keto-enol equilibria occurring in gas phase. Mass spectra of selected ketones and thioketones have been analysed and specific fragmentation assignments have been done to characterised and weigh co-existing keto and enol tautomers. Thioketones are of particular interest due to their tendency to shift the tautomeric equilibrium towards the enethiol form. The predictive value of this methodology is not only supported by the influence of these compounds nature and size of the substitution on these equilibria but also by the good correlation found between the selected fragments abundances ratio and semiempirical calculation (AM1) of the corresponding heats of tautomerization.