A study of some imidazo[l,5-a]benzodiazepin-6-ones by electron impact mass spectrometry. characterization by tandem mass spectrometry of a distonic fragment ion

The mass spectra of several imidazo[l,5-a]benzodiazepin-6-one derivatives of neuropharmacological significance were determined in order to establish their decomposition paths under electron impact. A novel distonic fragment ion was observed and it was possible to demonstrate by consideration of metastable ions and by tandem mass spectrometry that it undergoes isomerization to the corresponding classical structure.