Abstract

European Journal of Mass Spectrometry
Volume 10 Issue 6, Pages 747–754 (2004)
doi: 10.1255/ejms.683

A study of the methane catalyzed isomerization of HCO⁺ to HOC⁺ and the elimination of methane from metastable methoxymethyl cation

Travis D. Fridgen^*
Department of Chemistry, Wilfrid Laurier University, Waterloo, Ontario, Canada, N2L 3C5
John L. Holmes
Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada, K1N 6N5

Electronic structure calculations on the methane catalyzed HCO⁺/HOC⁺ potential energy surface have been conducted. The results show that 1,2-proton transfer from C to O can be efficiently catalyzed by CH₄. The complex CH₄/HCO⁺ and the closely related species, CH₅⁺/CO, are separated from the methoxymethyl cation CH₃OCH₂⁺ by a large potential energy barrier. It follows from the calculations that the metastable methoxymethyl cation is very unlikely to dissociate to yield HOC⁺. New experiments also show that HOC⁺ is not produced to any observable extent. A new explanation is proposed for the composite peak for m/z 29 observed from metastable dissociation of metastable methoxymethyl cation. The two components both arise from the formation of HCO⁺, but via different transition states. The minor, narrow, component involves dissociation from the CH₅⁺/CO complex and the broad peak from the CH₄/HCO⁺ ion-molecule complex.

Keywords: formyl cation, proton-transport catalysis, HOC⁺, metastable dissociaiton, computational chemistry, potential energy surface, methoxymethyl cation, isomerization

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