On the Theory of Oxidation-Reduction Reactions Involving Electron Transfer. III. Applications to Data on the Rates of Organic Redox Reactions

Abstract

A recently developed theory of oxidation-reduction reactions (Part I) is used to calculate the rates of organic redox reactions whose mechanism involves the transfer of an electron from one reactant to the other. The theory can be used to discuss factors affecting the rates of these reactions. These factors include a standard free energy of reaction, the Coulombic interaction of the ionic charges of the reactants and the solvation of the charged reactants. Attention is focused on the relation between the rate of the redox ~tep in the over-ail process and the standard free energy change, AfiO, of this step, rather than on the more usual but less fundamental one between the corresponding quantities of the over-all process itself. . An approximate method is described for applying the theory to a molecule whose charge is not located at Its center. Essentially ail organic molecules lie in this category.As an example of these considerations, several typical reactions are discussed. These reactions involve the oxidation of a series of hydroquinones by ferric ions and of a series of leucoindophenols by dissolved oxygen. They ~re assun;.ed ~o possess electron transfer, rather than atom transfer, mechanisms. Free energies and entropies of activatiOn of the redox step are calculated using the theoretical equation. The calculated results are considered to be in reasonable agreement with the experimental data, no adjustable parameters being employed.

Understanding the Heteroatom Effect on the Ullmann Copper-Catalyzed Cross-Coupling of X-Arylation (X = NH, O, S) Mechanism

“…The Gibbs free energy required to transfer the electron from the cooper complexes to the iodobenzene is significantly high, i.e., +107.0, +118.1, and +120.2 kcal/mol for 2-NH, 2-O and 2-S, respectively. The Gibbs energy barriers of this process were estimated using the Marcus-Hush theory [70][71][72][73][74][75][76][77] within the Saveant's model [78][79][80] for the SET coupled with the cleavage of the Ph-I bond (see the Supplementary Materials pages S2-S4 for details) [51]. The activation barriers obtained are +116.0, +131.9, and +135.1 kcal/mol for 2-NH, 2-O, and 2-S, respectively.…”

“…The Gibbs free energy required to transfer the electron from the cooper complexes to the iodobenzene is significantly high, i.e., +107.0, +118.1, and +120.2 kcal/mol for 2-NH, 2-O and 2-S, respectively. The Gibbs energy barriers of this process were estimated using the Marcus-Hush theory [70][71][72][73][74][75][76][77] within the Saveant's We next calculated the energy of the key steps for the most probable pathways for the formation of cross-coupling products PhXPh (3-X, X = NH, O, and S) starting with the complexes [(phen)Cu I (NHPh)], [(phen)Cu I (OPh)], and [(phen)Cu I (SPh)]. We considered only the four most appealed mechanisms displayed in Scheme 1.…”

ESR Spectroscopy of Nitroxides: Kinetics and Dynamics of Exchange Reactins

“…The theoretical aspects of electron transfer in solution originate in the 1950s with the pioneering work of Marcus [58][59][60], who offered a description of the energetics of both the self-exchange and the general reaction. Since then the theory has greatly evolved [61][62][63], as shall be discussed in the theoretical part of this chapter, where especially solvent (dynamic) effects are of interest.…”

Understanding Molecular Interactions within Chemically Selective Layered Polymer Assemblies

“…Structural integrity in the plane of the substrate is important for the growth of uniform layers on substrates that are intrinsically heterogeneous, such as silica. 12,13 Polymers also afford substantial structural regularity. While the formation of a polymeric interface can introduce mesoscopic disorder, the molecular scale regularity of alternating copolymers (AB) n allows substantial control over the density of specific functionalities in the polymer side groups.…”

“…The kinetics of AuNP formation can be understood in terms of Marcus electron transfer theory, [10][11][12][13] where the slower reactions proceed in the inverted region owing to the difference between the Au reduction potential and the amine oxidation potential. For certain of the amine reducing agents, after reduction of HAuCl 4 a subsequent reaction of the amine radical cation with other reducing agent molecules in solution forms poly(amine)s. These findings point collectively to the utility of amines as reducing agents in AuNP formation and provide information on the conditions under which these reactions will proceed.…”