Toward Infinite-Dilution Voltammetry

Lehmann, Mark W.; Evans, Dennis H.

doi:10.1021/jp982827+

Cited by 20 publications

(46 citation statements)

References 20 publications

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“…The first reduction peak for each compound, R 1 , is an overall two-electron process that is irreversible and diffusion controlled. For 1a (X = H) no additional reduction peaks were seen in scans to −3.1 V but for 1b (X = CN) a reversible couple (R 2 /O 2 ) appears with E ° equal to −2.87 V . This potential is identical with that found for reduction of p -cyanocumene, 2b .…”

Section: Resultssupporting

confidence: 73%

Cleavage Reactions of Radical Anions that Range from Homolytic to Heterolytic within the Same Family of Compounds

et al. 1999

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Properties of the radical anions of three R-nitrocumenes (R-nitrocumene, p-cyano-R-nitrocumene, and p-nitro-R-nitrocumene, 1a-c) have been determined by electrochemical methods. In particular, the standard potentials of the neutral/radical anion couples were found to be -2.20, -2.04, and -1.43 V with respect to the ferrocenium ion/ferrocene potential and the rate constants for expulsion of nitrite from the radical anions were 3 × 10 6 , 5 × 10 6 , and 240 s -1 for 1a-c, respectively. Comparison of these potentials with those of related compounds demonstrates that reduction of the nitroalkyl portion of the molecule occurs in 1a and 1b while in 1c the electron is added to the nitrophenyl group. Thus, using previously defined terminology, the cleavage of the radical anions of 1a and 1b to give nitrite and the corresponding cumyl radicals are examples of homolytic cleavage reactions but the cleavage of the radical anion of 1c is heterolytic. The driving force for the three cleavage reactions has been estimated and it is concluded that the large decrease in magnitude of the cleavage rate constants on going from 1a and 1b to 1c is mainly due to the much larger driving force for the first two.

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Section: Resultssupporting

confidence: 73%

Cleavage Reactions of Radical Anions that Range from Homolytic to Heterolytic within the Same Family of Compounds

et al. 1999

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“…Previous research has observed IP formation between solute ions and supporting electrolytes − or ionic liquids, and the measurements showed that the reduction potential was increased by this effect. − For example, the association free energy of the IP between TBA + and 9,9-dihexyl-9 H -fluorene-2-carbonitrile (F1CN) was measured to be −0.29 eV in tetrahydrofuran (THF) . Theoretical investigations by Fry − examined the structures and thermodynamics of various IPs.…”

Section: Resultsmentioning

confidence: 99%

Achieving Accurate Reduction Potential Predictions for Anthraquinones in Water and Aprotic Solvents: Effects of Inter- and Intramolecular H-Bonding and Ion Pairing

Zimmerman

2016

J. Phys. Chem. C

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In this combined computational and experimental study, specific chemical interactions affecting the prediction of one-electron and two-electron reduction potentials for anthraquinone derivatives are investigated. For 19 redox reactions in acidic aqueous solution, where AQ is reduced to hydroanthraquinone, density functional theory (DFT) with the polarizable continuum model (PCM) gives a mean absolute deviation (MAD) of 0.037 V for 16 species. DFT(PCM), however, highly overestimates three redox couples with a MAD of 0.194 V, which is almost 5 times that of the remaining 16. These three molecules have ether groups positioned for intramolecular hydrogen bonding that are not balanced with the intermolecular H-bonding of the solvent. This imbalanced description is corrected by quantum mechanics/molecular mechanics (QM/MM) simulations, which include explicit water molecules. The best theoretical estimations result in a good correlation with experiments, V(Theory) = 0.903V(Expt) + 0.007 with an R 2 value of 0.835 and an MAD of 0.033 V. In addition to the aqueous test set, 221 anthraquinone redox couples in aprotic solvent were studied. Five anthraquinone derivatives spanning a range of redox potentials were selected from this library, and their reduction potentials were measured by cyclic voltammetry. DFT(PCM) calculations predict the first reduction potential with high accuracy giving the linear relation, V(Theory) = 0.960V(Expt) − 0.049 with an R 2 value of 0.937 and an MAD of 0.051 V. This approach, however, significantly underestimates the second reduction potential, with an MAD of 0.329 V. It is shown herein that treatment of explicit ion-pair interactions between the anthraquinone derivatives and the cation of the supporting electrolyte is required for the accurate prediction of the second reduction potential. After the correction, V(Theory) = 1.045V(Expt) − 0.088 with an R 2 value 0.910 and an MAD value reduced by more than half to 0.145 V. Finally, molecular design principles are discussed that go beyond simple electron-donating and electron-withdrawing effects to lead to predictable and controllable reduction potentials.

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“…In a recent study, we determined the infinite-dilution standard potentials, E ° 1 and E ° 2 , for TCNQ (referred to the infinite-dilution standard potential for the ferrocene/ferrocenium couple) by using steady-state microelectrode voltammetry at low ionic strength in well-supported solutions (ratio of electrolyte to TCNQ concentration equal to 10). In the course of these studies, we noted an unusual asymmetry in the shape of the second steady-state voltammetric wave under certain experimental conditions.…”

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Effect of Comproportionation on Voltammograms for Two-Electron Reactions with an Irreversible Second Electron Transfer

and

Evans

1999

Anal. Chem.

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Many organic and organometallic compounds are reduced or oxidized in two steps with the addition or removal of the second electron occurring with greater difficulty than the first. In such EE reactions, a comproportionation reaction can occur in solution near the electrode by which the final product exchanges an electron with the reactant to form two molecules of the intermediate species. Normally, this comproportionation reaction has little or no effect in voltammetry. In this paper, a substantial effect of comproportionation is predicted for the case where the second electron-transfer reaction is irreversible. In steady-state voltammetry, the normally symmetric, sigmoid-shaped second wave is predicted to rise more sharply near its base than is observed in the absence of comproportionation and, in the limit of a very fast comproportionation reaction, an “onset potential” develops at which the current at the second wave increases abruptly from the limiting current of the first plateau. Experimental examples of these effects are presented for the reduction of tetracyanoquinodimethane in acetonitrile by steady-state microelectrode voltammetry, normal-pulse voltammetry, and cyclic voltammetry.

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Toward Infinite-Dilution Voltammetry

Cited by 20 publications

References 20 publications

Cleavage Reactions of Radical Anions that Range from Homolytic to Heterolytic within the Same Family of Compounds

Cleavage Reactions of Radical Anions that Range from Homolytic to Heterolytic within the Same Family of Compounds

Achieving Accurate Reduction Potential Predictions for Anthraquinones in Water and Aprotic Solvents: Effects of Inter- and Intramolecular H-Bonding and Ion Pairing

Effect of Comproportionation on Voltammograms for Two-Electron Reactions with an Irreversible Second Electron Transfer

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