The [CH5NO]+ ˙ potential energy surface: Distonic ions, lon-dipole complexes and hydrogen-bridged radical cations

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)(•+).

Differentiation of diastereomeric conduramine derivatives under electron ionization and chemical ionization mass spectral conditions

Diastereomeric conduramine derivatives, i.e., (1R,2S,3R/S,6S)-6-(N-carbomethoxyamino) 1,2-O-isopropylidenecyclohex-4-ene-1,2,3-triol (1 and 2) and their O-acetyl derivatives (3 and 4), were studied using gas chromatography (GC) with electron ionization (EI) and chemical ionization (CI). The EI mass spectra of diastereomeric pairs show consistent differences in the relative abundances of characteristic ions. The EI fragmentation patterns are based on precursor/product ion spectra, high-resolution mass spectrometry (HRMS) and deuterium labelling. The CI spectra show differences from the EI spectra, and the isobutane/CI spectra are much simpler than the methane/CI spectra. The differences shown in the CI spectra are similar to those shown in the product ion spectra of [M+H](+) ions generated under electrospray ionization (ESI) conditions. Theoretical calculations are performed to understand the observed differences. The differences in the relative stabilities of molecular ions, or protonated molecules at different sites, can explain the observed differences in the spectra.