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.

The formation of complexes by tetraethylresorcarene with planar guest ions studied by electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry

“…The complex formation was also studied with larger species, mesomeric betainium ions. The tendency of the betainium ions D 1 and D 2 to lose hydrogen from the exocyclic nitrogen, forming singly charged ions at m/z 360 and 405, respectively, was observed in our earlier study 14. The cleavage of a pyridine molecule or its replacement with a methanol molecule was also observed.…”

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“…161 Another recent study has examined the gas phase chemistry of related mesomeric heterocyclic betainium ions, 99, derived from 4-aminopyrimidine-2,6-bis(pyridinium) salts using FT-ICR mass spectrometry. 271 These ions are unreactive to reducing reagents and did not undergo substitution by aromatic or aliphatic amines. This low gas phase reactivity towards neutral reagents was ascribed to resonance stabilization.…”