The behavior of M+ and [M+H]+ ions of some oxoisoaporphines and quinolinone analogs

The mass spectrometric behaviour of some oxoisoaporphines and quinolinone analogs has been studied by both electrospray and electron ionization methods. By the former approach, information can be obtained on the decomposition pattern of the compounds under investigation in acidic condition, while by the latter the behaviour related to both cationic and radical character of molecular ion can be put in evidence. The collisional spectra of the protonated molecules indicate that protonation has taken place on both oxygen and nitrogen atoms. This can be justified by the fact that even if the most basic site present in the molecule is surely the N atom, in mass spectrometry conditions the protonation reactions are not governed by thermodynamics only, but kinetic effects can also play a fundamental role. Some exception to the even electron rule have been evidenced, and can be well justified by the high stability of the odd electron fragment ion. In electron ionization conditions fragmentation patterns well related to the original structures are present, allowing the characterization of isomeric compounds by the presence of specific fragmentation routes.