Publication
585
J.
Am. Chem. Soc., 126 (51), 16834-16840,
2004
DOI: 10.1021/ja045294t S0002-7863(04)05294-1 |
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Stepwise and Concerted Electron-Transfer/Bond Breaking
Reactions. Solvent Control of the Existence of Unstable  Ion Radicals and of the Activation Barriers of Their Heterolytic
Cleavage |
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Cyrille Costentin ,
Marc Robert and Jean-Michel Savéant*
Contribution from the Laboratoire d'Electrochimie Moléculaire, Unité Mixte
de Recherche Université, CNRS No. 7591, Université de Paris 7, Denis Diderot, 2
place Jussieu, 75251 Paris Cedex 05, France
*saveant
@laposte.net
Available data from various sources seem to indicate an important role of
solvation in the cleavage rates of intermediate ion radicals, in the passage from concerted to stepwise
electron-transfer/bond breaking reaction pathways and even in the very existence
of ion radicals. After preliminary computations treating the solvent as
dielectric continuum, these expectations are examined with the help of a simple
model system involving the anion radical of ONCH2Cl and two molecules
of water, which allows the application of advanced computational techniques and
a treatment of these solvent effects that emphasizes the role of solvent
molecules that sit close to the charge centers of the molecule. A ion radical minimum indeed appears upon introduction of the two water
molecules, and cleavage is accompanied by their displacement toward the leaving
anion, thus offering a qualitative mimicry of the experimental observations.
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