Publication
544
J. Am.
Chem. Soc., 123 (27), 11908
-11916, 2001
DOI: 10.1021/ja0117985 S0002-7863(01)01798-X |
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Stabilities of Ion/Radical Adducts in the Liquid Phase as Derived
from the Dependence of Electrochemical Cleavage Reactivities upon
Solvent
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Laurence Pause,
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
The idea that significant ion/radical interactions should vary with solvent if they do exist in the
liquid phase was pursued by an investigation of the dissociative electron-transfer reactivity of carbon tetrachloride
and 4-cyanobenzyl chloride in four different solvents, 1,2-dichloroethane, N,N-dimethylformamide, ethanol,
and formamide, by means of their cyclic voltammetric responses. Modification of the conventional dissociative
electron transfer theory to take account of an interaction between fragments in the ion/radical pair resulting
from the dissociative electron reaction allows a satisfactory fitting of the experimental data leading to the
determination of the interaction energy. There is an approximate correlation between the interaction energies
in the ion/radical pair and the solvation free energies of the leaving anion, Cl-. The interaction is maximal in
1,2-dichloroethane, which is both the least polar and the least able to solvate Cl-. The interaction is smaller
in the polar solvents, albeit distinctly measurable. The two protic solvents, ethanol and formamide, which are
the most able to solvate Cl-, give rise to similar interaction energies. The interaction is definitely stronger in
N,N-dimethylformamide, which has a lesser ability to solvate Cl- than the two other polar solvents. The existence
of significant ion/radical interactions in polar media is thus confirmed and a route to their determination opened.
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