Computational and experimental exploration of the gas-phase chemistry of alkyloxalate ions ROCOCOO− (R = H, CH3, C2H5, i-C3H7, and t-C4H9)

Alkyloxalate ions ROCOCOO− (R = H, CH3, C2H5, i-C3H7, and t-C4H9) are investigated by experiment and theory. Computational studies at the MP2/6-311++G(3df,3pd)//MP2/6-311++G(d) level of theory show that the structures vary with changing the size of the alkyl substituent R. Metastable ion and collisional activation mass spectra reveal three decomposition pathways of alkyloxalate ions corresponding to losses of CO and CO2 as well as a combined expulsion of CO and CO2. Decarbonylation dominates the spectra by far and leads to the corresponding alkylcarbonate ions ROCOO−. Two mechanisms are envisaged to understand this dissociation, and calculations suggest that the reaction proceeds through the formation of an intermediate ion-neutral complex.