Mass-spectrometric study of 2- and 4-azafluorenones

A mass-spectrometric study of 2- and 4-azafluorenones and their mono- and polymethyl derivatives showed that the presence of a methyl group in the benzene ring leads to a sharp increase in the relative intensity of the [M - H]+ ion peak. In contrast to the fragmentation of 2- and 4-azafluorenes, the mass spectra of monomethyl-substituted compounds do not contain an [M - CH3]+ fragment; this is probably associated with expansion of the pyridine or benzene ring to a seven-membered ring in the step involving the formation of the molecular ion due to inclusion of the methyl group. The intensity of the [M - CO]+ ion peak in the mass spectra of the 4-azafluorenones is higher by a factor of two with respect to the 2-azafluorenone isomers, and the [M - HCN]+ and [M - H, -HCN]+ ion peaks observed in the mass spectra of 2-azafluorenones are absent in them. © 1979 Plenum Publishing Corporation.