Mass spectrometric behaviour of cyclopentane-and cyclohexane-condensed pyrimidinediones under electron impact

Mass spectral fragmentations of four cyclopentane-condensed cis-pyrimidinediones and of six cyclohexane-condensed cis- or trans-pyrimidinediones were examined using metastable ion analyses and exact mass measurements. The fragmentation patterns of all of these compounds were clearly different and also cis- and trans-fused isomers were easy to distinguish from each other by their mass spectra. In spite of the differences in their mass spectral fragmentations, all compounds formed phenylisocyanates (m/z 119 and 153) and anilines (m/z 93 and m/z 127), the structures of which were verified by collision-induced dissociation experiments.