Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols.

Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols. Research Abstract Details 

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Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols. Abstract Text:

Ian J Rhile,Todd F Markle,Hirotaka Nagao,Antonio G DiPasquale,Oanh P Lam,Mark A Lockwood,Katrina Rotter,James M Mayer,

Three phenols with pendant, hydrogen-bonded bases (HOAr-B) have been oxidized in MeCN with various one-electron oxidants. The bases are a primary amine (-CPh(2)NH(2)), an imidazole, and a pyridine. The product of chemical and quasi-reversible electrochemical oxidations in each case is the phenoxyl radical in which the phenolic proton has transferred to the base, (*)OAr-BH(+), a proton-coupled electron transfer (PCET) process. The redox potentials for these oxidations are lower than for other phenols, predominately from the driving force for proton movement. One-electron oxidation of the phenols occurs by a concerted proton-electron transfer (CPET) mechanism, based on thermochemical arguments, isotope effects, and DeltaDeltaG(++)/DeltaDeltaG degrees . The data rule out stepwise paths involving initial electron transfer to form the phenol radical cations [(*)(+)HOAr-B] or initial proton transfer to give the zwitterions [(-)OAr-BH(+)]. The rate constant for heterogeneous electron transfer from HOAr-NH(2) to a platinum electrode has been derived from electrochemical measurements. For oxidations of HOAr-NH(2), the dependence of the solution rate constants on driving force, on temperature, and on the nature of the oxidant, and the correspondence between the homogeneous and heterogeneous rate constants, are all consistent with the application of adiabatic Marcus theory. The CPET reorganization energies, lambda = 23-56 kcal mol(-)(1), are large in comparison with those for electron transfer reactions of aromatic compounds. The reactions are not highly non-adiabatic, based on minimum values of H(rp) derived from the temperature dependence of the rate constants. These are among the first detailed analyses of CPET reactions where the proton and electron move to different sites.

Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols. Publishing Authors By Initials

IJ Rhile,TF Markle,H Nagao,AG DiPasquale,OP Lam,MA Lockwood,K Rotter,JM Mayer,

For similar natural sciences: physics: thermodynamics research abstracts see: natural sciences: physics: thermodynamics research

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Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols. Journal Published:

PUBLICATION TYPE: Research Support, N.I.H., Extr

Journal: Journal of the American Chemical Society

VOLUME: 128

Page Numbers: 6075-88

Journal Abbreviation: J. Am. Chem. Soc.

ISSN: 0002-7863

DAY: 10

MONTH: May

YEAR: 2006

Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols. Information

Number of References:

LANGUAGE: eng

NlmUniqueID: 7503056

Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols. Keywords Mesh Terms:

KEYWORDS: Thermodynamics

MESH TERMS: chemistry

Chemical & Substance for Abstract: Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols. Information

Substance Name: phenoxy radical

Registry Number: 3229-70-7

Grant and Affiliation Information for Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols.

AFFILIATION: Department of Chemistry, Campus Box 351700, University of Washington, Seattle, Washington 98195-1700, USA.

Country: United States

AGENCY: United States NIGMS

GRANT: 2 R01 GM50422

ACRONYM: GM

MEDLINETA: J Am Chem Soc

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