Structure and reactivity of molecular ions of isomeric pyrroloquinolinones and benzoquinolizinones.

The structure and mass spectrometric behaviour of molecular species of two benzo[ij]quinolizin-5-ones and one pyrrol[3,2,1-ij]quinolin-4-one were studied in detail with the aid of mass-analysed ion kinetic energy spectrometry and ion trapping experiments. Whereas in the usual electron impact spectra obtained with a double-focusing instrument clear differences are present among the three isomeric componds, the unimolecular fragmentation processes of the related M+. indicate the occurrence of isomerization processes to give a common structure. Significantly, under ion trap conditions nearly identical electron impact spectra are obtained; such unexpected behaviour was explained by either the presence of the buffer gas or the occurrence of different ionizing phenomena, leading to lower energy deposition in the molecular species. Under fast atom bombardment conditions, an acid-catalysed isomerization process occurs.