A series of alpha-chloro- and alpha-bromoketimines compounds (1-9) with different substituents at the alpha-position and at the imino group has been investigated by electron impact mass spectrometry as possible precursors of the correspondingly substituted alpha-imidoyl carbenium ion, an important class of destabilized carbenium ions. The main fragmentation of the molecular ions of compounds 1-9 in the ion source corresponds to an alpha-cleavage at the imino group; however, fragment ions are also formed by loss of the alpha-halo substituent. These fragment ions correspond at least formally to alpha-imidoyl carbenium ions. Their further reactions in dependence on the type of substituents at the imino group and at the alpha-C atom, were studied by mass-analysed ion kinetic energy and collisional activation mass spectrometry. The results agree with the initial formation of destabilized alpha-imidoyl carbenium ions but indicate an easy rearrangement of these ions in the presence of suitable alkyl substituents by 1,2- and 1,4-hydrogen shifts to more stable isomers.
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