Peculiarities of Mass Spectra of Substituted Pyrroloquinolines

The results of the mass spectrometric studies of a series of substituted isomeric pyrrolo[2,3-g], [3,2-f], [3,2-g], and [2,3-f]quinolines are presented and analyzed. Angular pyrroloquinolines with bulk peri substituents are less stable under electron ionization conditions than the corresponding linear isomers. The differences in the magnitude of the ratio of the intensity of a molecular ion peak to the total ionic current expressed as a percentage (WM) depend on the steric requirements of peri-located groups in angular systems. The data obtained make it possible to identify the structure of the resulting isomeric tricyclic heterosystems. A mechanism for the mass spectral decomposition of methyl-, phenyl-, methoxy-, hydroxyl-, and ethoxycarbonyl-substituted pyrroloquinolines is proposed.