Publication
557
J. Am.
Chem. Soc., 124 (45), 13533 -13539, 2002
DOI: 10.1021/ja0275212 S0002-7863(02)07521-2 |
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Dissociative Electron Transfer to Haloacetonitriles. An Example
of the Dependency of In-Cage Ion-Radical Interactions upon
the Leaving Group
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Annarita
Cardinale, Abdirisak A. Isse, Armando Gennaro, Marc Robert
and Jean-Michel Savéant
Contribution from the Dipartimento
di Chimica Fisica, Università di Padova, via
Loredan 2, 35131 Padova, Italy, and the Laboratoire
d'Electrochimie Moléculaire, Université de
Paris 7 - Denis Diderot, Case Courrier 7107, 2 place
Jussieu, 75251 Paris Cedex 05, France
The reductive cleavage of the haloacetonitriles (Cl, Br, I) in DMF provides
additional examples of the formation of a fragment cluster upon dissociative
electron transfer, which is able to survive in this polar solvent thanks
to the electron-withdrawing character of the cyano group. The remarkable
sensitivity of the activation energy to small changes of the interaction
energies allows, with help of the "sticky" dissociative electron-transfer
model, the precise determination of interaction energies down to a few
millielectronvolts from the cyclic voltammetric data. The interaction
energy rapidly decreases from Cl to Br and to I, correlated with the
increase of the halide radius. These observations add to the previously
gathered evidence to confirm the existence of such interactions and to
highlight their electrostatic character. This is further corroborated
by the quantum chemical computation of the potential energy profiles,
which exhibit a long-distance energy minimum. This revisiting of the
notion of  -ion
radicals and of their status in a polar medium makes them appear as an
electrostatic radical-ion pair rather than covalently bound molecules.
Their stability is a function of the Lewis acid-base properties of both
the radical and the leaving ion and is strongly influenced by the nature
of the solvent. |
