The extent of electron‐impact‐induced ring contraction in the formation of [M − CH3] fragments from N‐acetylpiperidine

This is the authors' abstract. We don't add key points for this paper.

In N‐acetylpiperidine, α‐carbon atoms (C‐2 or C‐6) of the ring have been recently identified as a source of loss of CH3 radicals from the molecular ion in addition to β‐carbon atoms (C‐3 or C‐5) and the acyl substituent (C‐8). Skeletal rearrangement by ring contraction to a five‐membered cyclic intermediate was invoked to be responsible for the expulsion of C‐2 or C‐6. Deuterium labelling suggested major and approximately equal contributions from the two losses of ring atoms as compared to an only minor contribution from loss of C‐8. 13C‐labelling of the latter now establishes the correctness of this inference, demonstrating that only 17% of the total loss of methyl arise from this position. Together with results of previous deuterium labelling this figure indicates that ring contraction contributes to the formation of [M − CH3] fragments to an extent of approximately 40%.