Protonated carbonic acid

Abstract

Protonated carbonic acid is generated by a consecutive elimination of a vinyl radical and an alkene from the radical cation of dialkylcarbonates. The properties of gaseous H₃CO⁺₃ have been established based on metastable ion studies supplementary to collision activation mass spectrometry, applying appropriate deuterium and/or ¹⁸O labelling. It is concluded that protonated carbonic acid is genrated as the symmetrical ‘ trihydroxy ’ species, whereas an unsymmetrical isomer is involved in the fragmentation proceses, primarily leading to protonated carbon dioxide and water. The existence of an equilibrium between the symmetrical and unsymmetrical isomers can be excluded. The thermochemical aspects of the H₃CO⁺₃ are discussed based on semiempirical MNDO calculations.