Gaseous Organic Dications: Molecules with Remarkable Properties

Abstract

Can small organic dications be generated in solution and/or the gas phase? What are the properties of these species with regard to their unimolecular chemistry (will they fall apart due to high Coulomb repulsion?) and their interaction with the solvent shell? What principles do they owe their existence to and what is the interplay of electrostatic repulsion versus binding energy? Answers to these and many other questions are provided by combined experimental/theoretical studies. In most cases pleasing agreement is observed which even includes the ionization energies of monocations from which dications are formed using charge-stripping mass spectrometry. Salient features of the doubly-charged cations are: 1) The often observed reversal of relative stabilities of isomers when compared with their neutral or mono-charged counterparts; 2) the significant structural changes which frequently favour anti-van't Hoff geometries; 3) the highly exothermic charge separation reactions which in the gas phase, however, are prevented by substantial barriers from occuring spontaneously, thus making observation of the thermochemically unstable dications feasible. The prospects of generating in solution any of the dications discussed are quite remote. Proton transfer from the dication to the solvent shell or addition of negatively charged species to the dication will occur avidly.