Structure and formation of [C4H6N]+ ions: 1—Ion structures derived from aliphatic nitriles

Structures and formation of the [C₄H₆N]⁺ ions present in the mass spectra of eleven α-substituted and eleven α-unsubstituted nitriles have been investigated from collisional activation and metastable ion spectra. Collisional activation spectra lead to identification of six structures. The [C₄H₆N]⁺ ions from some branched compounds prove to be mixtures. This, as well as the identity of all metastable ion parameters and certain spectral data, shows that energy differences between all structures are small. This is corroborated by MINDO/3 calculations showing a spread from 724 to 891 kJ mol^?1 over the structures. Earlier proposals for two different [C₄H₆N]⁺ ion structures, based on the mass spectra of deuterium labelled compounds, appeared to be correct. A computer program to calculate the contribution of standard spectra in a measured spectrum has been developed.