Hammett Substituent Effect on the Cleavage Rate Constants of Anion Radicals in Dimethylformamide

Jaworski, Jan S.

doi:10.1039/a702186k

Cited by 4 publications

(5 citation statements)

References 14 publications

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“…Values of D , the theoretical limiting current for the one-electron reduction of 9-ArCl, n eff , and k at each temperature are recorded in Table . k at room temperature was observed to be in reasonable agreement with values of k for halide bond cleavage of 9-ArCl in the same solvent medium, namely, 200, 260, and 165 s -1 reported by Wipf and Wightman, M'Halla et al, and Jaworski et al, respectively.…”

Section: Resultssupporting

confidence: 86%

“…Second, we describe application of this technique in the determination of activation parameters for the halide bond cleavage of o -bromonitrobenzene and 9-chloroanthracene. Both species undergo rapid halide bond cleavage via a two-electron transfer process probably via an ECE-type process. − …”

Section: Introductionmentioning

confidence: 99%

“…Both species undergo rapid halide bond cleavage via a two-electron transfer process probably via an ECE-type process. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]…”

Section: Introductionmentioning

confidence: 99%

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Variable-Temperature Microelectrode Voltammetry: Application to Diffusion Coefficients and Electrode Reaction Mechanisms

Jacob

Coles

et al. 1999

J. Phys. Chem. B

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An apparatus for the measurement of steady-state microelectrode voltammetry at elevated temperatures is described. The scope of this experimental approach as a method for the determination of diffusion coefficients at variable temperatures in the case of simple one-electron processes is demonstrated. Diffusion coefficients over a range of temperatures are derived for N,N,N‘,N‘-tetramethylphenylenediamine in both acetonitrile and water solvents, tris-4-bromophenylamine in acetonitrile, and ferrocene in acetonitrile and dimethylformamide from which activation energies for diffusion are obtained. Diffusion coefficient values are used to derive Stokes−Einstein radii for each species in solution. The electroreductions of o-bromonitrobenzene in dimethylformamide and 9-chloroanthracene in acetonitrile are studied as a function of temperature and activation energies estimated for carbon−halide bond cleavage in the corresponding radical anions.

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Section: Resultssupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

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Variable-Temperature Microelectrode Voltammetry: Application to Diffusion Coefficients and Electrode Reaction Mechanisms

Jacob

Coles

et al. 1999

J. Phys. Chem. B

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“…Protonation rate constants were measured as previously 10 by fitting to the theoretical curve the experimental shift of the voltammetric peak potential E p with the scan rate v for irreversible electroreduction of anthracene in the presence of phenols. The theoretical curve was obtained 18,19 neglecting the ohmic drop, assuming the DISP1 mechanism [Eqns (1)-(4)] and pseudo first order for the rds reaction (2) established in solutions of 20-100-fold excess of phenol and described by the unimolecular rate constant k. An example of that fitting for anthracene and three phenols is shown in Fig.1; E is the reversible redox potential for the couple hydrocarbon-its radical anion, i.e. for reaction (1) in the absence of any proton donor, F and R are Faraday and gas constants, respectively, and T ¼ 298 K is the temperature of measurements.…”

Section: Resultsmentioning

confidence: 99%

Kinetics of protonation of anthracene radical anions in DMSO by a series of substituted phenols

Jaworski

Cembor

2003

J of Physical Organic Chem

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The rate constants k H for proton transfer from a series of substituted phenols to anthracene radical anions formed in DMSO were measured by the voltammetric method. A quadratic Brønsted dependence of RT lnk H against pK a of phenols was observed. The intrinsic activation barrier ÁG 0 z calculated on the basis of the known pK a value for the conjugate acid ArH . of the anthracene radical anion is the same as for the reaction in DMF. The homolytic bond dissociation energy (for ArH . ! Ar þ H .) was also found to be the same as in DMF. The results obtained are in full agreement with theoretical predictions for protonation of radical anions forming C-H acids, described as the concerted electron and H atom transfer.

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“…The protonation rate constant was measured by fitting to the theoretical curve the experimental shift of the voltammetric peak potential E p with the scan rate ν for the irreversible electroreduction of anthracene and phenanthrene in the presence of phenols. A theoretical curve was obtained 23, 24 neglecting the ohmic drop, assuming the DISP1 mechanism (1)-( 4) and the pseudo first-order of the rds reaction (2), established in solutions of 20 to 100-fold excess of phenol and described by the unimolecular rate constant k. An example of that fitting for the anthracene and three phenols is shown in Fig. 1; EЊ is the reversible redox potential for the couple: hydrocarbon/its radical anion, i.e.…”

Section: Resultsmentioning

confidence: 99%

Kinetics of protonation of anthracene and phenanthrene radical anions in DMF by a series of substituted phenols. Comparison of Brønsted and Hammett plots

Jaworski¹

1999

J. Chem. Soc., Perkin Trans. 2

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The rate constants k H for the proton transfer from a series of substituted phenols to anthracene and phenanthrene radical anions formed in DMF have been measured by the voltammetric method. The quadratic Brønsted dependencies of RT ln k H against pK a of phenols for both radical anions were observed. For the conjugate acid ArH ؒ of the anthracene radical anion pK a is known and the intrinsic activation barrier ∆G o ‡ = 59 kJ mol Ϫ1 was calculated. The homolytic bond dissociation energy D for ArH ؒ →Ar ϩ H ؒ was evaluated and the obtained value of D/4 = 51 kJ mol Ϫ1 is in good agreement with the theoretical prediction ∆G o ‡ = (D ϩ λ o )/4 (where λ o is the solvent reorganization energy) based on a recent theory of the deprotonation of radical cations described as a concerted electron and H atom transfer. However, linear Hammett plots of log k H against σ were observed for both radical anions and the lack of a quadratic effect was explained as a result of a through-resonance contribution. On the other hand, the application of normalized substituent constants σ o resulted in the quadratic Hammett plots in accordance with the Reactivity Selectivity Principle.

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Hammett Substituent Effect on the Cleavage Rate Constants of Anion Radicals in Dimethylformamide

Cited by 4 publications

References 14 publications

Variable-Temperature Microelectrode Voltammetry: Application to Diffusion Coefficients and Electrode Reaction Mechanisms

Variable-Temperature Microelectrode Voltammetry: Application to Diffusion Coefficients and Electrode Reaction Mechanisms

Kinetics of protonation of anthracene radical anions in DMSO by a series of substituted phenols

Kinetics of protonation of anthracene and phenanthrene radical anions in DMF by a series of substituted phenols. Comparison of Brønsted and Hammett plots

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