Characteristic Activity Parameters of Electron Donors and Electron Acceptors

Abstract

It is well-known that for an electron transfer reaction, the electron-donating ability of electron donors and the electron-accepting ability of electron acceptors can be quantitatively described by the oxidation potential of electron donors and the reduction potential of electron acceptors. However, for an electron transfer reaction, the electron-donating activity of electron donors and the electron-accepting activity of electron acceptors cannot be quantitatively described by a characteristic parameter of electron donors and a characteristic parameter of electron acceptors till now. In this paper, a characteristic activity parameter of electron donors and electron acceptors named as their thermo-kinetic parameter is proposed to quantify the electron-donating activity of electron donors and the electron-accepting activity of electron acceptors in electron transfer reactions. At the same time, the thermo-kinetic parameter values of 70 well-known electron donors and the corresponding 70 conjugated electron acceptors in acetonitrile at 298 K are determined. The activation free energies of 4900 typical electron transfer reactions in acetonitrile at 298 K are estimated according to the thermo-kinetic parameter values of 70 electron donors and 70 conjugated electron acceptors, and the estimated results have received good verification of the corresponding independent experimental measurements. The physical meaning of the thermo-kinetic parameter is examined. The relationship of the thermo-kinetic parameter with the corresponding redox potential as well as the relationship of the activation free energy with the corresponding thermodynamic driving force of electron transfer reactions is examined. The results show that the observed relationships between the thermo-kinetic parameters and the redox potentials as well as the observed relationships between the activation free energy and the thermodynamic driving force depend on the choice of electron donors and electron acceptors as well as the electron transfer reactions. The greatest contribution of this paper is to realize the symmetry and unification of kinetic equations and the corresponding thermodynamic equations of electron transfer reactions.