In order to arrange hydrocarbons and solvents in series in accordance with their donor-acceptor power it is necessary to separate out from the total heat of mixing the energy characterizing specific interaction between donor and acceptor molecules. However, no satisfactory correlation has yet been established between the donor-acceptor properties of solvents and the thermodynamic functions of mixing with hydrocarbons. The enthalpy of mixing is a reliable experimental characteristic of interactions in solution.
The review should thus serve to complement other recent reviews which have dealt with electron-transfer kinetics on a broader basis. The overall goal of the review is to provide a unified picture of the combined capabilities of modern quantum chemistry in yielding accurate quantitative measures of the strength of electronic coupling and at the same time providing compact models for understanding the coupling in terms of the concepts of molecular bonding and electronic structure. As much as possible, the present review deals with purely electronic aspects of electron transfer, although attention is drawn to vibronic factors as deemed necessary. The recent review of solid-state electron-transfer processes by Mikkelsen and Ratner dealt also with situations of more extended electronic states which may be important in periodic environments. He confines his attention to cases of relatively weakly interacting more » donor/acceptor systems where, indeed, the occurrence of localized states may be safely assumed. For the most part the author is able to deal with models based on discrete molecular clusters (either large molecules or supermolecules) consisting of localized donor, acceptor, and intervening bridging sites. The experimental data which provides the impetus for most of the theoretical work addressed here pertains predominantly to condensed-phase systems involving disorder (i.e., nonperiodic) media. The specific focus of this review is to survey recent progress in the application of theoretical and computational techniques of quantum chemistry to the elucidation of electronic factors controlling donor/acceptor interactions in electron-transfer reactions.
0 kommentar(er)
