Mass spectrometry as a valuable tool for the study of tautomerism of amides and thioamides

Abstract

Mass spectra of some amides and thioamides under different sample introduction temperatures and ionization electron energies are reported and analysed along with the corresponding theoretical calculations. The influence of temperature on the imidol/amide selected fragments abundance ratio (for different amides and for different pair of ions of the same amide whenever possible) are studied and employed to estimate the enthalpy change for the tautomeric equilibria. The same analysis is reported for different electron energies obtaining comparable results despite the impact on relative ion fragments abundances. AM1 molecular orbital calculations not only support that tautomerism in the mass spectrometer is negligible after ionization of the selected amides but also render a means to determine the theoretical heat of reaction which are well correlated with the experimental values.