Electron impact induced fragmentation of alkyl(benzylidene)amines

Abstract

The mass spectral decomposition reactions of alkyl(benzylidene)amines (Schiff's bases) have been investigated with the aid of deuterium labelling, high resolution measurements, and metastable defocusing. The most significant results are (a) cleavage of the C(4)–C(5) bond (δ-cleavage) with formation of five-membered ring fragment ions is very much favoured over other C–C bond fissions; (b) very abundant C₇H₇⁺ ions are formed through skeletal rearrangement processes, joining the phenyl group to the α-methylene group of the alkyl fragment; and (c) very abundant (M–C₆H₅) and (M–C₆H₆) ions are formed at low voltage from benzylidene(butyl)amine and the labelled analogues, the C₆H₆ neutral fragment eliminated incorporating the methine hydrogen atom. Ring closure is suggested to accompany the formation of both ions; similar fragmentations take place to a much lesser extent in the fragmentation of other alkylimines.