Electron ionization and electrospray ionization mass spectrometric study of a series of isomeric N-chloro(or bromo)benzyl-substituted (E)-2'(3'- or 4')-hydroxy-4-stilbazole halides

Abstract

The electron ionization (EI) mass spectra and electrospray ionization (ESI) mass spectra of a series of isomeric N-chlorobenzyl- and N-bromobenzyl-substituted (E)-2'(3' or 4')-hydroxy-4-stilbazole chlorides and bromides (1-12) were recorded. The fragmentation pathways of all of the compounds and the characteristic fragment ions formed by EI-MS were studied by means of B/E and B(2)/E constant linked-scanning techniques. The formation of ions originating from preionization reactions, characteristic of quaternary halides under EI-MS conditions, such as the elimination of chloro- or bromobenzyl halides, dehydrohalogenation or substitution reactions, is explained. As soft ionization methods cause no such degradation reactions, the ESI-MS spectra of the studied compounds were also obtained for comparison. We thus demonstrated the applicability of EI-MS even in cases when preionization takes place, as long as such secondary processes are properly accounted for.