The dissociation chemistry of ionized methyl carbamate and its isomers revisited: theory and experiment in concert.

Early combined computational and experimental studies by J.K. Terlouw c.s. in Refs. 1-3 propose that low-energy methyl carbamate ions, NH(2)COOCH(3)(•+) (MC-1), rearrange into distonic ions NH(2)C(OH)OCH(2)(•+) and hydrogen-bridged radical cations [NH(2)C=O--H--OCH(2)](•+) (MC-5) en route to the observed losses of HCO(•) and CO. In this study, we report on the generation of ions MC-5 by decarbonylation of ionized methyl oxamate NH(2)COCOOCH(3)(•+). Theory and experiment agree that ion MC-5 is a key intermediate in the dissociation of low-energy ions MC-1. The subsequent HCO(•) loss, however, may not proceed via the route proposed in Ref. 2, but rather by an entirely different mechanism involving proton-transport catalysis (PTC) in ion MC-5. This view is further supported by the dissociation behaviour of the MC-5 isotopologue [ND(2)C=O--D--OCH(2)](•+), which is conveniently generated from the d(3)-labelled glycolamide ion DOCH(2)C(=O)ND(2)(•+).