Theory of Electron Transfer Reactions: Insights and Hindsights

Sutin, Norman

doi:10.1002/9780470166314.ch9

Cited by 713 publications

(193 citation statements)

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“…In terms of predicting a HAT rate constant to within a factor of 5, one can usually ignore other effects such as hydrogen tunneling, nonadiabatic behavior, and precursor complex formation. The success of the CR, in this and other applications, may partially be a result of its inherent averaging, as pointed out by Sutin (7).…”

Section: (Si Text) This Reaction Is Much Slower Than H-atom Abstractmentioning

confidence: 87%

“…The CR, and the Marcus theory of electron transfer (ET) from which it is derived, applies to unimolecular reactions of weakly bound precursor and successor complexes (7). In ET reactions, these complexes are typically weakly associated, and their energies are often estimated with a simple electrostatic calculation.…”

Section: (Si Text) This Reaction Is Much Slower Than H-atom Abstractmentioning

confidence: 99%

“…1) to the two degenerate self-exchange rate constants (k XH∕X• and k YH∕Y• ), the equilibrium constant (K XH∕Y• ¼ k XH∕Y• ∕k YH∕X• ), and the frequency factor (f ). The variable f is defined as lnðf Þ ¼ ½lnðK XH∕Y• Þ∕4 lnðk XH∕X• k YH∕Y• Z −2 Þ, with the collision frequency Z typically taken as 10 11 M −1 s −1 (7). For transition metal complexes, Eq.…”

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confidence: 99%

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Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

Warren

Mayer

2010

Proc. Natl. Acad. Sci. U.S.A.

112

137

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Chemical reactions that involve net hydrogen atom transfer (HAT) are ubiquitous in chemistry and biology, from the action of antioxidants to industrial and metalloenzyme catalysis. This report develops and validates a procedure to predict rate constants for HAT reactions of oxyl radicals (RO • ) in various media. Our procedure uses the Marcus cross relation (CR) and includes adjustments for solvent hydrogen-bonding effects on both the kinetics and thermodynamics of the reactions. Kinetic solvent effects (KSEs) are included by using Ingold's model, and thermodynamic solvent effects are accounted for by using an empirical model developed by Abraham. These adjustments are shown to be critical to the success of our combined model, referred to as the CR/KSE model. As an initial test of the CR/KSE model we measured self-exchange and cross rate constants in different solvents for reactions of the 2,4,6-tri-tert-butylphenoxyl radical and the hydroxylamine 2,2′-6,6′-tetramethylpiperidin-1-ol. Excellent agreement is observed between the calculated and directly determined cross rate constants. We then extend the model to over 30 known HAT reactions of oxyl radicals with OH or CH bonds, including biologically relevant reactions of ascorbate, peroxyl radicals, and α-tocopherol. The CR/KSE model shows remarkable predictive power, predicting rate constants to within a factor of 5 for almost all of the surveyed HAT reactions.free radicals | Marcus theory | proton-coupled electron transfer | reactive oxygen species | oxyl radicals H ydrogen atom transfer (HAT) reactions (Eq. 1) have been a cornerstone of organic and biological chemistry for over a century (1, 2). These reactions are key steps in many important processes, from energy conversion to the chemistry of reactive oxygen species and antioxidants (3). Thus, developing a detailed understanding of the factors that dictate HAT reactivity has long been a goal.A large number of HAT rate constants have been measured in many laboratories with various techniques (4, 5). Rates of HAT reactions have traditionally been understood by using the BellEvans-Polanyi (BEP) relation, which relates the activation energy to the enthalpic driving force (6). Whereas the BEP relation holds well within sets of similar reactions, a comprehensive theoretical understanding of HAT is still emerging (3).Our group has been exploring the use of the Marcus cross relation (CR) Eq. 2 (7), a corollary of the Marcus theory of electron transfer, as the basis for a general model for HAT rates (8)(9)(10)(11)(12). This use of the CR grew out of recognizing HAT as one class of a larger set of reactions in which one electron and one proton are transferred (, termed proton-coupled electron transfer. In this paper, we use "HAT" to refer to any reaction in which H • is transferred from a donor to an acceptor in a single kinetic step (Eq. 1), although other definitions have been used (13).The CR, with respect to HAT reactions, relates the cross rate constant (k XH∕Y• , Eq. 1) to the two degenerate self-exchange rate c...

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Section: (Si Text) This Reaction Is Much Slower Than H-atom Abstractmentioning

confidence: 87%

Section: (Si Text) This Reaction Is Much Slower Than H-atom Abstractmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

Warren

Mayer

2010

Proc. Natl. Acad. Sci. U.S.A.

112

137

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“…In the simplest form of the theory, the free energy of the reduced and oxidized states has the same harmonic dependence on a reaction coordinate for solvent reorganization (such as local dielectric constant of the solvation shell), before and after electron transfer. For the same redox reaction above, the reaction rates take the form [4,9,26],…”

Section: Introductionmentioning

confidence: 99%

Simple formula for Marcus–Hush–Chidsey kinetics

Zeng

Smith

Bai

et al. 2014

Journal of Electroanalytical Chemistry

105

153

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The Marcus-Hush-Chidsey (MHC) model is well known in electro-analytical chemistry as a successful microscopic theory of outer-sphere electron transfer at metal electrodes, but it is unfamiliar and rarely used in electrochemical engineering. One reason may be the difficulty of evaluating the MHC reaction rate, which is defined as an improper integral of the Marcus rate over the Fermi distribution of electron energies. Here, we report a simple analytical approximation of the MHC integral that interpolates between exact asymptotic limits for large overpotentials, as well as for large or small reorganization energies, and exhibits less than 5% relative error for all reasonable parameter values. This result enables the MHC model to be considered as a practical alternative to the ubiquitous Butler-Volmer equation for improved understanding and engineering of electrochemical systems.

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“…The situation worsens further as the high temperature approximation is not always valid, meaning that corrections for quantum-mechanical tunnelling should be included. This was pointed out by Holstein [64], and used by several other authors like Bixon and Jortner [61,65], and Sutin [66] yielding an equation of the following type: 4 () t a n h 4…”

Section: Theorymentioning

confidence: 97%