Chemistry of Protonated Species in Gaseous Environments

An overview is presented of gas-phase studies on the structure and reactivity of protonated species from the authors’ research. Specific problems have been addressed operating in different gaseous environments, either in radiolytic systems at atmospheric pressure, enabling the NMR characterization of the neutral end products of gas phase ion–molecule reactions, or in low-pressure FT-ICR mass spectrometry, where ions can be trapped and characterized by their reactivity or spectroscopic features. Proton transfer reactions have revealed the role of competing acidic sites leading to biologically relevant C7H7O radical species and of competing basic sites in substituted benzenes. Proton transfer reactions have also been used as a tool to form elusive cations, e.g. c-C3H7+, modulating the reaction energetics, and to unveil the structure and occurrence of degenerate isomerization processes within the benzenium ion.