Benzene Radical Ion in Equilibrium with Solvated Electrons

Marasas, Richard A.; Iyoda, and Tomokazu; Miller, John R.

doi:10.1021/jp026893u

Cited by 27 publications

(39 citation statements)

References 56 publications

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“…Notably, this VBE value is roughly reached already without any explicit ammonia molecules, which suggests that the continuum dielectric environment is sufficient to semi-quantitatively describe the solvent stabilization of the benzene radical anion. This is also in line with the observed stability in other polar solvents that were used in experimental studies 10,11 and that have similar dielectric constants to that of liquid ammonia. The above result is in a quantitative agreement with more accurate but also more compu- The VBEs calculated by QM-MM (bottom) or QM-EFP (middle) method for the resolvated clusters varying by the overall size (x-axis) and by the size of the inner QM subsystem (differently colored curves).…”

Section: Discussionsupporting

confidence: 87%

Benzene Radical Anion Microsolvated in Ammonia Clusters: Modelling the Transition from an Unbound Resonance to a Bound Species

Kostal,

Brezina,

Marsalek

et al. 2021

Preprint

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The benzene radical anion, well-known in organic chemistry as the first intermediate in the Birch reduction of benzene in liquid ammonia, exhibits intriguing properties from the point of view of quantum chemistry. Notably, it has the character of a metastable shape resonance in the gas phase, while measurements in solution find it to be experimentally detectable and stable. In this light, our previous calculations performed in bulk liquid ammonia explicitly reveal that solvation leads to stabilization. Here, we focus on the transition of the benzene radical anion from an unstable gas-phase ion to a fully solvated bound species by explicit ionization calculations of the radical anion solvated in molecular clusters of increasing size. The computational cost of the largest systems is mitigated by combining density functional theory with auxiliary methods including effective fragment potentials or approximating the bulk by polarizable continuum models. Using this methodology, we obtain the cluster size dependence of the vertical binding energy of the benzene radical anion converging to the value of −2.3 eV at a modest computational cost.

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Section: Discussionsupporting

confidence: 87%

Benzene Radical Anion Microsolvated in Ammonia Clusters: Modelling the Transition from an Unbound Resonance to a Bound Species

Kostal,

Brezina,

Marsalek

et al. 2021

Preprint

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“…-100 J/mol.K. 40 Using a pulse radiolysis -time resolved conductivity method, Holroyd 39 (2) is at the lower end of this range; for mononitriles the standard entropies are unprecedentedly low. To our knowledge, electron attachment reactions with such extremely low standard entropy have never been observed, in any liquid.…”

Section: Resultsmentioning

confidence: 99%

Toward Electron Encapsulation: Polynitrile Approach

Shkrob

Sauer

2006

J. Phys. Chem. A

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This study seeks an answer to the following question: Is it possible to design a supramolecular cage that would "solvate" the excess electron in the same fashion in which several solvent molecules do that co-operatively in polar liquids? Such an "encapsulated electron" would be instrumental for structural and dynamics studies of electron solvation and might be useful for molecular electronics. Two general strategies are outlined for "electron encapsulation," viz. electron localization using polar groups arranged on the (i) inside of the cage or (ii) outside of the cage. The second approach is more convenient from the synthetic standpoint, but it is limited to polynitriles. We demonstrate, experimentally and theoretically, that this second approach faces a formidable problem: the electron attaches to the nitrile groups forming molecular anions with bent C-C-N fragments. Since the energy cost of this bending is very high, for dinitrile anions in n-hexane, thebinding energies for the electron are very low and for mononitriles, these binding energies are lower still, and the entropy of electron 2. attachment is anomalously small. Density functional theory modeling of electron trapping by mononitriles in n-hexane suggests that the mononitrile molecules substitute for the solvent molecules at the electron cavity, "solvating" the electron by their methyl groups.We argue that such "solvated electrons" resemble multimer radical anions in which the electron density is shared (mainly) between C 2p orbitals in the solute/solvent molecules, instead of existing as cavity electrons. The way in which the excess electron density is shared by such molecules is similar to the way in which this sharing occurs in large diand poly-nitrile anions, such as 1,2,4,5,7,8,10,11-octacyano-cyclododecane -. The work thus reveals limitations of the concept of "solvated electron" for organic liquids: it might be impossible to draw a clear line between such species and a certain class of radical anions. It also demostrates the feasibility of "electron encapsulation."

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“…The dissociation constant Kd = 6.75x10 -11 M for (BzPh -• ,Na + ) pairs is very small, even smaller than that reported for (Benzene -• ,Na + ), Kd = 4.5x10 -10 M. 28 An attempt to check this very low Kd by DC conductivity of (BzPh -• ,Na + ) in THF gave only an upper limit, Kd ≤ 1.0x10 -9 M. Conductivity could not confirm that it is as small as the value deduced from the free energy cycle because of uncertainties due to residual conductivity arising from traces of water. Support for this value will come from measurements on the effects of other ions and computed values of ∆Gd° reported below.…”

Section: Resultsmentioning

confidence: 65%

Effects of electrolytes on redox potentials through ion pairing

Bird

Iyoda

Bonura

et al. 2017

Journal of Electroanalytical Chemistry

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Reduction potentials have been determined for two molecules, benzophenone (BzPh) and perylene (Per), effectively in the complete absence of electrolyte as well as in the presence of three different supporting electrolytes in the moderately polar solvent THF. A description of how this can be so, and qualifications, are described in the discussion section. The primary tool in this work, pulse radiolysis, measures electron transfer (ET) equilibria in solution to obtain differences in redox potentials. Voltammetry measures redox potentials by establishing ET equilibria at electrodes, but electrolytes are needed for current flow. Results here show that without electrolyte the redox potentials were 100-451 mV more negative than those with 100 mM electrolyte. These changes depended both on the molecule and the electrolyte. In THF the dominant contributor to stabilization of radical anions by electrolyte was ion pairing. An equation was derived to give changes in redox potentials when electrolyte is added in terms of ion pair dissociation constants and activity coefficients. Definite values were determined for energetics, ∆G d°, of ion pairing. Values of ∆Gd° for pairs with TBA + give some doubt that it is a "weaklycoordinating cation." Computations with DFT methods were moderately successful at describing the ion paring energies. I.

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Benzene Radical Ion in Equilibrium with Solvated Electrons

Cited by 27 publications

References 56 publications

Benzene Radical Anion Microsolvated in Ammonia Clusters: Modelling the Transition from an Unbound Resonance to a Bound Species

Benzene Radical Anion Microsolvated in Ammonia Clusters: Modelling the Transition from an Unbound Resonance to a Bound Species

Toward Electron Encapsulation: Polynitrile Approach

Effects of electrolytes on redox potentials through ion pairing

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