285seen in Figure 7, the presence of another factor is suggested to affect the reaction rates of the present oxidation. It is speculated that the most favorable steric conditions are met in the case of n = 1 for the attack of Ce(V). For example, the methyl group in AO+-CH3 may be directed toward the inside of surfactant layer. As a result, the carbon atom Cg, which is considered to be the site attacked by Ce(1V) ion, is exposed toward the water phase. On the other hand, the interaction of AOH+ with surfactant molecules is mostly due to the dispersive force between n-electron groups. Thus the benzene ring in AOH+ is faced with the surfactant layer to result in the blocking of the Cg atom by the bulky surfactant molecules. These steric factors may cause the higher reactivity of AO+--CH3 as well as the lower reactivity of AOH+ than expected from their hydrophobicity scale.
Acknowledgment.Reverse pulse voltammetry is applied to the quantitative treatment of second-order chemical reactions following reversible electron transfer. Simple algebraic and graphical procedures based on the results of simulations are employed to estimate the backward rate constant of the chemical reaction from an approximation to the equilibrium constant (K'J which is obtained experimentally. One iteration produces accurate values of the forward and backward rate constants and the true equilibrium constant as shown by detailed fitting of experimental results to simulated results. For the following dimerization of N-methyl-2-carbomethoxypyridinyl radical the technique yields values of K = 104.e8 M-', kf = 104.03 M-' s-l. The treatment is applicable for -1.3 5 log (K'C) I 4.
IntroductionPrevious work has described the technique of reverse pulse polarography (RPP) (or reverse pulse vo1tammetry)l and its application to the study of homogeneous reactions coupled with electron-transfer processes.24 The purpose of this paper is to describe the quantitative treatment of RP data for second-order following reactions. To our knowledge the case of reversible following dimerization reactions has not been treated b e f~r e .~ Consider the reaction sequence
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