The mass spectra of pyrimidines. II. 2(1H)-Pyrimidinethiones and some N(1)-substituted derivatives

The EI induced fragmentation of 2(1H)-pyrimidinethione (1), some N(1)-substituted derivatives, and 2(1H)-pyrimidineselenone (4) have been studied. Principal fragmentation pathways have been identified using 2H-labelling, metastable defocussing, and exact mass measurements.The fragmentations of 1 and 4 generally parallel those reported for 2(1H)-pyrimidinone. In contrast to the oxo-compound, however, direct expulsion of the exocyclic hetero atom is significant in the fragmentation of 1, and dominates the spectrum of 4.Based on metastable peak abundances and kinetic energy release measurements, it is postulated that the [M – H]+ entity generated from N-ethyl-2-pyrimidinethione has a thiazolinium structure.