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

Abstract

Early combined computational and experimental studies by J.K. Terlouw and colleagues propose that low-energy methyl carbamate ions, NH 2COOCH 3 •+ (MC-1), rearrange into distonic ions NH 2C(OH)OCH 2 •+ and hydrogen-bridged radical cations [NH 2C=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 2COCOOCH 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 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 [ND 2C=O-D-OCH 2] •+, which is conveniently generated from the d 3-labelled glycolamide ion DOCH 2C(=O)ND 2 •