The one-electron reduction potential of 4-substituted phenoxyl radicals in water

Lind, Johan; Shen, X.; Eriksen, Trygve E.; Merényi, Gábor

doi:10.1021/ja00158a002

Cited by 353 publications

(339 citation statements)

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“…68 The correlation in Figure 2 coupled with the linear free energy relationship upon which the σ p + constants are based can therefore be interpreted as reflecting the ability of the substituent to inductively and/or resonantly stabilize the oxygen radical via the modulation of charge density within the molecule.…”

Section: Resultsmentioning

confidence: 99%

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Fehir

McCusker

2009

J. Phys. Chem. A

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We have carried out a theoretical study of a series of para-substituted phenoxy radicals in an effort to understand the factors influencing spin and charge density distribution in open-shell systems. The calculations reveal that the distribution of spin and charge are not correlated: cases were found for which spin and charge move together, whereas for other substituents the two quantities exhibit spatially distinct intramolecular polarizations. Charge density variations across the series were found to correlate well with both the Hammett (σ p ) and Hammett-Brown (σ p + ) constants for each substituent, indicating that inductive and/or resonance effects are primarily responsible for the polarization of charge within the molecule. In contrast, the distribution of unpaired spin density could not be adequately accounted for using any of the typical Hammett-type spin delocalization constants cited in the literature. We uncovered an empirical correlation between the polarization of spin density and the R-HOMO-R-LUMO gap of the substituted phenoxy radicals: this led to the development of a simple model based on a three-electron, two-orbital bonding scheme in which mixing between the HOMO of the substituent and the SOMO of the phenoxy moiety serves to define the nature and extent of unpaired spin polarization throughout the molecule. This analysis yielded a correlation coefficient of r > 0.97 for the 15 substituents examined in the study; spin polarization effects in compounds that exhibited the greatest deviation from this correlation could also be readily explained within the context of the model. The underlying reason for the ability to differentially polarize spin and charge likely stems from the fact that net unpaired spin density is completely carried by the unpaired electron (and thus tracks the spatial characteristics of the SOMO), whereas charge density reflects the behavior of all of the electrons of the system. These results could have implications in the field of molecular magnetism, suggesting a means for synthetically tuning the magnitude of intramolecular exchange interactions, as well as providing guidance for the design of catalysts for radical-radical coupling reactions.

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Section: Resultsmentioning

confidence: 99%

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Fehir

McCusker

2009

J. Phys. Chem. A

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“…As shown in Eq. 1, pK a (II) and the one-electron reduction potential of compound I, E o (I), determine the dissociation energy, D (O−H), of the newly formed FeO−H bond of compound II (40)(41)(42). Thus, both pK a (II) and E o (I) are important in determining the C−H bond activation capability of APO-I.…”

Section: Significancementioning

confidence: 99%

Heme-thiolate ferryl of aromatic peroxygenase is basic and reactive

Wang

Ullrich

Hofrichter

et al. 2015

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

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A kinetic and spectroscopic characterization of the ferryl intermediate (APO-II) from APO, the heme-thiolate peroxygenase from Agrocybe aegerita, is described. APO-II was generated by reaction of the ferric enzyme with metachloroperoxybenzoic acid in the presence of nitroxyl radicals and detected with the use of rapidmixing stopped-flow UV-visible (UV-vis) spectroscopy. The nitroxyl radicals served as selective reductants of APO-I, reacting only slowly with APO-II. APO-II displayed a split Soret UV-vis spectrum (370 nm and 428 nm) characteristic of thiolate ligation. Rapid-mixing, pHjump spectrophotometry revealed a basic pK a of 10.0 for the Fe IV −O−H of APO-II, indicating that APO-II is protonated under typical turnover conditions. Kinetic characterization showed that APO-II is unusually reactive toward a panel of benzylic C−H and phenolic substrates, with second-order rate constants for C−H and O−H bond scission in the range of 10-10 7 M −1 ·s −1 . Our results demonstrate the important role of the axial cysteine ligand in increasing the proton affinity of the ferryl oxygen of APO intermediates, thus providing additional driving force for C−H and O−H bond scission.

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“…HA as in equation-6 (HA = PhOH or PhNH 2 ). The standard free energy ∆ G 0 is calculated in eq-7, from the known E 0 and K a values [78,79] and is taken to be equal to ∆ H …”

Section: Discussionmentioning

confidence: 99%

Permanganate Oxidation mechanisms of Alkylarenes

Chauhan¹

2014

IOARJAC

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The one-electron reduction potential of 4-substituted phenoxyl radicals in water

Cited by 353 publications

References 1 publication

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Differential Polarization of Spin and Charge Density in Substituted Phenoxy Radicals

Heme-thiolate ferryl of aromatic peroxygenase is basic and reactive

Permanganate Oxidation mechanisms of Alkylarenes

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