Evidence for the formation of acyclic ions from the radical cations and cyclic ions from the protonated molecules of ¿,¿-diamines upon loss of ammonia

The structural characterization of the ions generated by the electron ionization-induced loss of ammonia from the molecular ions of α,ω-diamines, using ion/molecule reactions in combination with collision-induced dissociation (CID) studies, is described. The results of the experiments of ion/molecule reactions using dimethyl disulfide exclude the distonic radical cation structure for those long-lived ions proposed earlier by other authors for ions generated within a few microseconds following ionization. The unimolecular and CID characteristics of the ions [M---NH3]√+ of 1,4-diaminobutane and 1,5-diaminopentane and of their fragment ion m/z=56, are discussed in terms of the structures CH3CH2CH=CHNH2√+ and CH3CH2CH2CH=CHNH2√+ for the ions [M---NH3]√+, respectively. The structure of the closed shell ions resulting from loss of ammonia from the protonated α,ω-diamines was also probed through the CID spectra of model ions prepared by chemical ionization with methane in the chemical ionization source of the mass spectrometer.