Are Anion Radicals Nucleophiles and/or Outersphere Electron Donors? An Ab Initio Study of the Reaction of Ethylene and Formaldehyde Anion Radicals with Methyl Fluoride and Chloride

Bertrán, Juan; Gallardo, Iluminada; Moreno, Miquel; Savéant, b Jean-Michel

doi:10.1021/ja953679t

Cited by 27 publications

(39 citation statements)

References 30 publications

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“…This is in agreement with an outer-sphere electron transfer, as usually described in the literature for this type of reaction. [17][18][19] Direct electrolysis is also reported in the table, and the distribution of dichlorobenzenes does not show any significant difference when compared with the mediated approach. Only a poorer current efficiency is noted in the former.…”

Section: Mediated Electrolysis Of 124-trichlorobenzene-electrolysismentioning

confidence: 94%

Mediated Approach for the Electrochemical Reduction of Chlorobenzenes in Nonaqueous Media

Guena

Wang

Gattrell

et al. 2000

J. Electrochem. Soc.

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The use of a range of mediators for the partial or complete dechlorination of a series of polychlorinated benzenes has been investigated. The dechlorinations were carried out in acetonitrile, and the products were analyzed by gas chromatography-mass spectroscopy (GC-MS). The partial dechlorination using organic mediators was successful and good control of the reaction (i.e., monodechlorination) and good efficiency could be achieved. Some mediators showed poor current efficiencies due to the lower stability of their anion radical in the presence of protons. The monodechlorination of trichlorobenzene with four different mediators showed that the product distribution in terms of initial chlorine removed was little affected by the mediator used. This product distribution has also been investigated for the whole series of polychlorobenzenes. Polydechlorination using a single mediator was tried using biphenyl, anthracene, and dibenzofuran. After passing enough charge to completely dechlorinate trichlorobenzene, few chlorinated benzenes remained in solution and less than the expected amount of benzene was detected. The was explained by nonvolatile products undetected by GC-MS. It is suggested that when higher overpotential mediators are used, the reaction shifts to produce higher molecular weight products by radical-radical coupling reactions. Biphenyl might be a convenient mediator for the dechlorination of polychlorobenzene or even polychlorobiphenyl.

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Section: Mediated Electrolysis Of 124-trichlorobenzene-electrolysismentioning

confidence: 94%

Mediated Approach for the Electrochemical Reduction of Chlorobenzenes in Nonaqueous Media

Guena

Wang

Gattrell

et al. 2000

J. Electrochem. Soc.

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“…On the other hand, theoretical considerations have indicated that the transition state of inner-sphere ET reactions involving just a few kcal mol Ϫ1 of interaction may be quite well-ordered. [21][22][23][24][25][26][27][28][29][30] Experimentally, the extraction of activation entropies from Arrhenius plots did reveal that they were larger (i.e. less negative) for the reactions of aromatic radical anions with sterically hindered alkyl and benzyl halides than for the reactions with the simple halides, where the S N 2 component was present.…”

Section: Introductionmentioning

confidence: 98%

Activation parameters for the competing electron transfer and SN2 pathways of the reaction of anthracene radical anion with cyclopropylmethyl bromide

Jensen

Sørensen

Pedersen

et al. 2002

J. Chem. Soc., Perkin Trans. 2

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The reaction between the electrogenerated radical anion of anthracene and alkyl halides has been studied in the temperature interval of Ϫ50 to 40 ЊC in N,N-dimethylformamide in order to describe in detail the competition between the electron transfer (ET) and S N 2 pathways. For cyclopropylmethyl bromide the competition can be quantified directly on the basis of an analysis of the distribution of ring-opened versus ring-closed products. In general, the ET pathway is found to prevail although the S N 2 pathway becomes of greater importance as the temperature is lowered. When the product analysis is combined with the measurement of the overall rate constant for the reaction the pertinent activation parameters can be extracted for both mechanisms. As expected ∆H ‡ S N 2 is smaller than ∆H ‡ ET (by 7 kJ mol Ϫ1 ) because of the stronger bonding interaction present in the transition state of S N 2. On the other hand, this effect is more than counterbalanced by the fact that ET is entropically favoured because of smaller geometrical restrictions (∆S ‡ ET Ϫ ∆S ‡ S N 2 = 37 J mol Ϫ1 K Ϫ1 ). The S N 2 mechanism leads to substitution in the 9 position of anthracene while for the ET mechanism it takes place in all three positions of 1, 2 and 9. The overall distribution of products in the three positions is largely independent of temperature. This is due to the fact that the increased amount of S N 2 products formed in the 9 position as the temperature is lowered is accompanied by an equally large decrease in the amount of ET products obtained in the very same position. Exactly the same constancy in the product distribution is seen for the reaction of anthracene radical anion with bromoethane, where both mechanisms also exist. For the reaction involving the sterically hindered 1-iodoadamantane, on the other hand, the S N 2 pathway is precluded and in this case there is a profound decrease in the amount of 9-substitution as the temperature is lowered.

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“…A well-known example of the latter case is the reaction between ketyl radical anions and alkyl halides in which both electron transfer (ET) products and substitution at carbon (Sub(C)) products can be formed via the same, tightly bound transition state. [3][4][5][6][7][8][9][10][11][12][13][14] Such cases are especially attractive, since a slight change of the potential energy surface around the transition state may vary the branching ratio of the products.…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5][6][7][8][9][10][11][12][13][14] Electron transfer can occur through two pathways. In one case, an electron can be transferred via an outer sphere species which involves a weak interaction and surface hopping.…”

Section: Introductionmentioning

confidence: 99%

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A Single Transition State Serves Two Mechanisms. The Branching Ratio for CH₂O^•- + CH₃Cl on Improved Potential Energy Surfaces

Shaik

Schlegel

2006

J. Phys. Chem. A

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The reaction of formaldehyde radical anion with methyl chloride, CH 2 O •-+ CH 3 Cl, is an example in which a single transition state leads to two products: substitution at carbon (Sub(C), CH 3 CH 2 O • + Cl -) and electron transfer (ET, CH 2 O + CH 3• + Cl -). The branching ratio for this reaction has been studied by ab initio molecular dynamics (AIMD). The energies of transition states and intermediates were computed at a variety of levels of theory and compared to accurate energetics calculated by the G3 and CBS-QB3 methods. A bond additivity correction has been constructed to improve the Hartree-Fock potential energy surface (BAC-UHF). A satisfactory balance between good energetics and affordable AIMD calculations can be achieved with BH&HLYP/6-31G(d) and BAC-UHF/6-31G(d) calculations. Approximately 200 ab initio classical trajectories were calculated for each level of theory with initial conditions sampled from a thermal distribution at 298 K at the transition state. Three types of trajectories were distinguished: trajectories that go directly to ET product, trajectories that go to Sub(C) product, and trajectories that initially go into the Sub(C) valley and then dissociate to ET products. The BH&HLYP/6-31G(d) calculations overestimate the number of nonreactive and direct ET trajectories because the transition state is too early. For the BH&HLYP and BAC-UHF methods, about one-third of the trajectories that initially go into the Sub(C) valley dissociate to ET products, compared to just over half with UHF/6-31G(d) in the earlier study. This difference can be attributed to a better value for the calculated energy release from the initial transition state and to an improved Sub(C) f ET barrier height with the BH&HLYP and BAC-UHF methods.

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Are Anion Radicals Nucleophiles and/or Outersphere Electron Donors? An Ab Initio Study of the Reaction of Ethylene and Formaldehyde Anion Radicals with Methyl Fluoride and Chloride

Cited by 27 publications

References 30 publications

Mediated Approach for the Electrochemical Reduction of Chlorobenzenes in Nonaqueous Media

Mediated Approach for the Electrochemical Reduction of Chlorobenzenes in Nonaqueous Media

Activation parameters for the competing electron transfer and SN2 pathways of the reaction of anthracene radical anion with cyclopropylmethyl bromide

A Single Transition State Serves Two Mechanisms. The Branching Ratio for CH₂O^•- + CH₃Cl on Improved Potential Energy Surfaces

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Are Anion Radicals Nucleophiles and/or Outersphere Electron Donors? An Ab Initio Study of the Reaction of Ethylene and Formaldehyde Anion Radicals with Methyl Fluoride and Chloride

Cited by 27 publications

References 30 publications

Mediated Approach for the Electrochemical Reduction of Chlorobenzenes in Nonaqueous Media

Mediated Approach for the Electrochemical Reduction of Chlorobenzenes in Nonaqueous Media

Activation parameters for the competing electron transfer and SN2 pathways of the reaction of anthracene radical anion with cyclopropylmethyl bromide

A Single Transition State Serves Two Mechanisms. The Branching Ratio for CH2O•- + CH3Cl on Improved Potential Energy Surfaces

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A Single Transition State Serves Two Mechanisms. The Branching Ratio for CH₂O^•- + CH₃Cl on Improved Potential Energy Surfaces