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 and colleagues propose that low-energy methyl carbamate ions, NH2COOCH3 center dot+ (MC-1), rearrange into distonic ions NH2C(OH)OCH2 center dot+ and hydrogen-bridged radical cations [NH2C=O-H-OCH2](center dot+) (MC-5) en route to the observed losses of HCO center dot and CO. In this study, we report on the generation of ions MC-5 by decarbonylation of ionized methyl oxamate NH2COCOOCH3 center dot+. Theory and experiment agree that ion MC-5 is a key intermediate in the dissociation of low-energy ions MC-1. The subsequent HCO center dot loss, however, may not proceed via the route proposed by Terlouw et al., 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 [ND2C=O-D-OCH2](center dot+), which is conveniently generated from the d(3)-labelled glycolamide ion DOCH2C(=O)ND2 center dot+