Electron and proton transfer reactions of simple aldehyde and ketone radical cations and their enol and distonic isomers

Abstract

The reactivity of the keto and enol isomers of the acetaldehyde and acetone radical cations and the keto, enol and distonic isomers of the propanal radical cation was examined in the gas phase by using Fourier-transform ion cyclotron resonance mass spectrometry. The results obtained show that these radical cations do not readily undergo isomerization within a gas-phase collision complex. Further, the ions favor electron transfer to proton transfer whenever the former reaction is thermodynamically accessible. This reaction can occur either directly by abstraction of an electron by the radical cation or indirectly by a more complex mechanism that is likely to involve energetically favorable proton and hydrogen atom transfers within the ion-molecule complex (a H +/H shuttle). The above knowledge can be utilized in the differentiation of the keto, enol, and distonic isomers of simple carbonyl-containing radical cations.