Cyclization of Dimethyl Oxalate upon Electron Impact

Article abstract of DOI:10.1002/oms.1210160110

Isotope labelling experiments and also consecutive fragmentation investigations of metastable ions, a novel technique in mechanistic studies, have been carried out to elucidate structure and genesis of the m/z 45 ions from dimethyl oxalate as well as dimethyl carbonate.It is shown that the formation of the m/z 45 ions, CH3O(1+)=CH2, in the mass spectra of these compounds arises via single step processes.Mechanisms involving hydrogen transfer and subsequent formation of cyclic intermediates which then collapse to give CH3O(1+)=CH2 directly from molecular ions are suggested.No evidence was found for a two-step fragmentation route to m/z 45 from the molecular ions of either dimethyl oxalate or dimethyl carbonate.