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Tautomerism And Mass Spectra Of Thiomorpholides

Eduardo A.Castro, Patricia E.Allegretti, Facundo Namor, Jorge J.P.Furlong

The mass spectra of N,N-disubstituted thioamides generated by GC/ MS can provide valuable information about keto-enol equilibria occurring in gas phase. Mass spectra of selected thiomorpholides have been analysed and specific fragmentation assignments have been done to characterised and weigh co-existing keto and enol tautomers. The predictive value of this methodology is not only supported by the influence of substitution nature and size of these compounds 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. The results show that the thioketo-thioenol equilibrium can be studied by mass spectrometry where ionization in the ion source has a negligible effect on the position of that equilibrium and by GC/ MS where solvent separation in the analytical column seems to preclude shifts from the equilibrium reached at the injection port of the gas chromatograph.