Mass spectrometry of analogues of pyrimidine bases: 2- and 4-alkylthio-5-halogenouracils

The electron impact induced mass fragmentations of 16 new 2- and 4-alkylthio-5-chloro- and 2- and 4-alkylthio-5-bromouracils are presented. The elucidation of the fragmentation pathways is described. The fragmentation routes have been confirmed by accurate mass measurements and metastable transitions. It has been found that the position of uracil ring thiation may be deduced on the basis of the mass spectral fragmentation patterns.