Evidence for extensive recombination of the ring-opened to the original cyclic molecular ions of 2-substituted piperidines and pyrrolidines after electron impact

Abstract

The unusually preferred formation of (M– alkyl)⁺ ions by α-fission of 2,2-dialkyl-substituted N-ethylpiperidines (2) and -pyrrolidines (3) and the virtual absence of ring degradation products is caused by facile recombination of the ring-opened to the original cyclic molecular ions. Suppression of ring opening of the initially formed molecular ions or conversion of the ring-opened into other isomeric molecular ions as explanations of the mass spectrometric behaviour of (2) and (3) are excluded.