Electron-impact induced fragmentation of three-membered heterocycles. Part III. N-t-alkylaziridine-1-carboxamides

Abstract

A comparative study of the electron-impact induced fragmentation of four N-t-alkylaziridine-1-carboxamides has been undertaken by conventional and high-resolution mass spectrometry. The main paths of fragmentation can be interpreted in terms of the unrearranged molecular structure. The base peak in all aziridinecarboxamides is due to elimination of a t-alkyl isocyanate from the molecular ion, involving rearrangement of the N–H hydrogen to the aziridine nitrogen atom. α-Cleavage, with ejection of one of the alkyl groups attached to the tertiary carbon, is a major competing process. Fission of both the CO–NH bond and the CO–aziridine bond occurs, leading to isocyanate and aziridinium-type ions, respectively. There is no compelling evidence to indicate common intermediates in the fragmentation of an aziridinecarboxamide and the structural isomer N-t-alkylimidazolidin-2-one. Based on mass spectral evidence, the diaziridinone → aziridinecarboxamide isomerization is not reversible.