Mass spectrometry of tautomeric compounds. Part IV. Structure of the molecular ions of 4-hydroxycoumarins

Abstract

The structure of the mass spectral molecular ions of 4-hydroxycoumarins is discussed. From the fact that variation of inlet temperatures did not affect the spectral patterns, the molecular ion is considered not to be an equilibrium mixture of keto and enol forms. In contrast to earlier proposals, the enolic nature of the molecular ion is demonstrated by comparison of the spectra with those of acetylated derivatives and by deuterium-labelling experiments.