Destabilized carbenium ions: α‐imidoyl carbenium ions and the electron impact mass spectra of α‐haloaldimines and α‐haloketimines

Abstract

AbstractA series of α‐chloro‐ and α‐bromoketimines compounds (1‐9) with different substituents at the α‐position and at the imino group has been investigated by electron impact mass spectrometry as possible precursors of the correspondingly substituted α‐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 α‐cleavage at the imino group; however, fragment ions are also formed by loss of the α‐halo substituent. These fragment ions correspond at least formally to α‐imidoyl carbenium ions. Their further reactions in dependence on the type of substituents at the imino group and at the α‐C atom, were studied by mass‐analysed ion kinetic energy and collisional activation mass spectrometry. The results agree with the initial formation of destabilized α‐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.