CHARACTERIZATION AND DIFFERENTIATION OF HETEROCYCLIC ISOMERS .3. STUDY OF HIGH INTERNAL ENERGY IONS PRODUCED BY ELECTRON IONIZATION MASS-SPECTROMETRY ON 3-METHYL-1,2-THIAZOLOPYRIDINE AND 2-METHYL-1,3-THIAZOLOPYRIDINE

The eight members of two classes of heterocyclic isomers, namely 3-met hyl-1,2-, 1a-d and 2-methyl-1,3-thiazolopyridines 2a-d have been chara cterized by mass spectrometry under electron ionization. High internal energy ions formed in the source have been studied by low and high re solution mass spectrometry. The data show remarkable differences among the various components of each class depending on the position of the nitrogen in the pyridine ring. Furthermore, by comparing the mass spe ctra of members of series 1 with those of their corresponding isomers belonging to series 2, it is still possible to obtain evidence for dif ferent behaviors in the fragmentation pathways. It seems to exclude th e occurrence of interconversion phenomena from one isomer into another , as well as conversion to a common intermediate before fragmentation. This also suggests that each member of series 1 and 2 retains its own structure after electron ionization. The data obtained on a doable fo cusing instrument equipped with electrostatic and magnetic analyzers h ave been compared with those obtained on a mass spectrometer with an i on trap as the analyzer.