Marcus Theory for Outer-Sphere Heterogeneous Electron Transfer:  Predicting Electron-Transfer Rates for Quinones

Abstract

Steady-state voltammetry is used to measure the heterogeneous electron-transfer rates for the reduction of quinones to determine the dependence of k 0 on molecular size, according to Marcus theory. This dependence is then used to predict the electron-transfer rate constants of related quinones, and the predictions are compared to experimental measurements.

Electrochemical Rate Constants in Room Temperature Ionic Liquids: The Oxidation of a Series of Ferrocene Derivatives

“…[ [33][34][35][36] A mean value for the heterogeneous rate constant for the oxidation of ferrocene in [C 2 To determine whether the relationship between the hydrodynamic radius, r, and the heterogeneous rate constant, k 0 , which has been observed for ferrocene derivatives in MeCN, [36] applies in the case of RTILs, the formal hydrodynamic radii in Equation (6) have been estimated by using the Stokes-Einstein equation: [46] r ¼ kT PphD ð6Þ…”

“…[29] The high-speed channel electrode (HSChE) has been used successfully in several studies in conventional organic solvents to measure electron kinetics [30,31] and electron transfer. [32][33][34][35][36] High flow rates over a microband electrode are obtained by pressuring a chamber containing the solution and the electrode assembly up to 1.5 atmospheres. To accomplish a range of different flow rates combinations of chamber pressure and capillary diameter are used.…”

“…[31,37] This system was also employed to investigate the validity of Marcus theory for outersphere heterogeneous electron transfer in alkyl cyanide solvents. [33][34][35][36] It was shown that the rate of electron transfer of a single compound in different alkyl cyanides is determined by the longitudinal dielectric relaxation properties of the solvent, while differences in outer sphere rate between a series of similar compounds in MeCN can be quantitatively rationalised by considering their relative hydrodynamic radii as predicted by the Marcus theory. [38][39][40][41][42] The aim herein is to employ the high-speed channel electrode system to measure the heterogeneous rate constants, k 0 , for a series of ferrocene derivatives in RTILs and to asses the results in the light of Marcus theory.…”

Hydrodynamic voltammetry at membrane-covered electrodes

“…With regard to the rate of charge transfer, for the 0.1 lm pore diameter PET membrane, the peak-to-peak separations were predominantly in the range 0.060-0.065 V. This indicates that the electron transfer process was rapid on the cyclic voltammetric time-scale, as would be anticipated for a quinone molecule in an aprotic solvent [27]. The relatively low peak-to-peak separation also suggests that the ohmic compensation applied largely counteracted bulk solution and membrane resistance.…”

ESR Spectroscopy of Nitroxides: Kinetics and Dynamics of Exchange Reactins

“…Another approach has been suggested by Compton and co-workers [70,71] who, instead of calculated radii, use experimentally determined hydrodynamic radii.…”