Abstract
Mass spectra of 1-methyl (or phenyl)-1 H-pyrazolo[3, 4-d] pyrimidine (Io), 4-substituted-1-methyl (or phenyl)-1 Hpyrazolo [3, 4-d] pyrimidines (Ia to Ie) and 4-substituted-4, 5-dihydro-1-methyl-1H-pyrazolo [3, 4-d] pyrimidines (II) were examined. The main fragmentation of I proceeds by two dissociation paths. One is the formation of pyrazolo [3, 4-d] pyrimidinium cation1or the molecular ion of Io caused by the elimination of4-substituent. And the fragmentation of condensed pyrimidine ring of the resulting ion I or Io leads to pyrazolyne radical ion 3 by the loss of hydrogen cyanide or cyano radical in successive steps. Another is the formation of cyclic ion (8, 9 and 14) or diazatropyrium type ion (5' and 10') caused by the migration of 4-substituent with the loss of hydrogen radical. The loss of diazomethyl or diazophenyl radical originated from the condensed pyrazole ring at the first step is peculiar to mass spectra of1-methyl (or phenyl)-4-phenyl-1H-pyrazolo [3, 4-d] pyrimidine (Ie). The main fragmentation of II is the elimination of 4-substituent to form pyrazolo [3, 4-d] pyrimidinium ion 20.
