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Abstract

The electron impact (EI) ionization-induced fragmentation pathways of the new 1,9-bis(dimethylamino) phenalenium cation [1]+ were investigated. The peri-dimethylamino substituents of [1]+ are incorporated in a trimethine cyanine substructure and show strong steric interactions. A mechanism is proposed for the unusual elimination of CH3N[DOUBLE BOND]CH2, HN(CH3)2 and (CH3)3N from [1]+ and for the accompanying cyclizations to heterocyclic ions: prior to fragmentation, the intact cation [1]+ rearranges, by reciprocal CH3 and H transfers, to new isomeric cations which decompose subsequently in a characteristic way. A wealth of consistent information on dissociation pathways and fragment structures is provided by collision-induced dissociation tandem mass spectra, collision-induced dissociation mass-analysed ion kinetic energy spectra and exact mass measurements of the salt cation and of its primary fragment ions. The liquid secondary ion mass spectrum of [1]+ is very similar to its EI mass spectrum.