Fragmentation studies of tetrahydropyridocarbazole derivatives by EI, ESI-MS/MS and FAB

Four tetrahydropyridocarbazole derivatives were analysed by different mass spectrometry techniques: electrospray ionization, fast atom bombardment and by low and high resolution 70 eV electron ionization. Retro Diels Alder is the main fragmentation pathway, whereas other pathways leading to [M—1]+, [M—CH3]+ and double charge ions also occur to considerable extents. Semi-empirical calculation provided some evidence on the nature of tropylium ions [M—1]+. Calculation of ΔHf0 indicated that [M+—1] could be formed preferentially when a hydrogen atom is lost from the methyl substituent of the homoaromatic ring.