Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Study of Mesomeric Heterocyclic Betainium Ions

Abstract

Mesomeric heterocyclic betainium ions derived from 4-aminopyrimidine-2,6-bis(pyridinium) salts, were examined in the gas phase by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionisation. The purpose of the study was to clarify the general gas-phase properties and reactions of these novel ions. Collision-induced dissociation (CID) was used to investigate fragment ion formation and fragmentation pathways. The ions have an unusual tripolar structure with one negative and two positive charges that are in cross-conjugation within a common -electron system. Resonance stabilisation within the ions makes them relatively unreactive in ion–molecule reactions under the conditions in the FT-ICR cell. CID spectra showed that the charged pyridinium groups are easily lost as neutral pyridine. Otherwise the fragmentation depends on the substituent on the aniline moiety.