REACTIONS WITHIN AND BETWEEN ADJACENT DIMETHYLAMINO GROUPS - COLLISION-INDUCED DISSOCIATION TANDEM MASS-SPECTROMETRIC STUDY OF THE 1,9-BIS(DIMETHYLAMINO)PHENALENIUM CATION

The electron impact (EI) ionization-induced fragmentation pathways of the new 1,9-bis(dimethylamino) phenalenium cation [1]+ were investigat ed. 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=CH2, HN(CH3 )2 and (CH3)3N from [1]+ and for the accompanying cyclizations to hete rocyclic ions: prior to fragmentation, the intact cation [1]+ rearrang es, by reciprocal CH3 and H transfers, to new isomeric cations which d ecompose subsequently in a characteristic way. A wealth of consistent information on dissociation pathways and fragment structures is provid ed by collision-induced dissociation tandem mass spectra, collision-in duced 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.