The gas-phase decarbonylation of the N-methyl- and N,N-dimethylacetamide radical cations gives rise to the α-distonic isomers of the dimethylamine and trimethylamine molecular ions by transfer of the acetyl methyl to nitrogen in two steps: H transfer and CH₂ transfer. Complete exchange af all carbon-bonded hydrogen atoms precedes loss of acetyl radicals or of ketene from the metastable amide molecular ions. The reactions are examined with deuterium labeling and with composite ab initio methods of the G3 family.

Keywords: gas-phase ion chemistry, ab initiocalculations, unimolecular reactions, ionized methylacetamides, α-distonic ions, extrusion reactions, reaction mechanism, MIKE spectra, deuterium labeling