Sticky Dissociative Electron Transfer to Polychloroacetamides. In-Cage Ion−Dipole Interaction Control through the Dipole Moment and Intramolecular Hydrogen Bond

Abstract

The reductive cleavage of chloro- and polychloroacetamides in N,N-dimethylformamide gives new insights into the nature of the in-cage ion radical cluster formed upon dissociative electron transfer. Within the family of compounds investigated, the electrochemical reduction leads to the successive expulsion of chloride ions. At each stage the electron transfer is concerted with the breaking of the C-Cl bond and acts as the rate-determining step. The reduction further leads to the formation of the corresponding carbanion with the injection of a second electron, which is in turn protonated by a weak acid added to the solution. From the joint use of cyclic voltammetric data, the sticky dissociative electron-transfer model and quantum ab initio calculations, the interaction energies within the cluster fragments (*R, Cl-) resulting from the first electron transfer to the parent RCl molecule are obtained. It is shown that the stability of these adducts, which should be viewed as an essentially electrostatic radical-ion pair, is mainly controlled by the intensity of the dipole moment of the remaining radical part and may eventually be strengthened by the formation of an intramolecular hydrogen bond, as is the case with 2-chloroacetamide.

Application of the dissociative electron transfer theory and its extension to the case of in-cage interactions in the electrochemical reduction of arenesulfonyl chlorides

“…[28][29][30][31][32]35,[69][70][71][72][73] This rules out the occurrence of a stepwise mechanism, and tends to indicate the presence rather of a concerted process. The nature of this initial electron transfer will be further investigated below.…”

“…3 shows the LUMOs of compounds 1a-g and the SOMOs of their reduced forms (radical anions or radical/anion pairs). [28][29][30][31][32][33][34]36 For compounds 1a-e, the LUMOs are more located on the S-Cl group with a lower factor on the aryl moiety, indicating that the extra electron is most likely injected directly into the s S-Cl bond leading to or concomitant with its dissociation. The SOMOs corresponding to their reduced forms are also more localized on the S-Cl group (s radical anion or radical/ion pair) and provide thus more support to the injection of the extra electron into the s S-Cl bond.…”

“…The factors controlling the ET mechanism variation as well as the extend of the in-cage interactions between the reduction fragments are discussed on the basis of the dissociative ET theory and its extension to the case of in-cage interactions (''sticky'' dissociative ET). [28][29][30][31][32][33][34]64 Theoretical calculations help rationalize both the difference in the ET mechanism as well as the cluster formation. Electrochemical measurements were conducted in three electrode glass cells, thermostatted at 25 1C, and under dry nitrogen.…”

Passage from Stepwise to Concerted Dissociative Electron Transfer through Modulation of Electronic States Coupling

“…Several experimental works have confirmed the reality of such interactions and the applicability of the model. These examples mostly concerned heterogeneous reactions [18] but examples of homogeneous electron transfer have also been found. [19] Thus, this effect can be considered to be at the origin of the D ap values obtained in this study.…”

Study of the electrochemical reduction of amoebicide teclozan and its amperometric determination in pharmaceutical formulations

“…The literature provides several discussions about concerted and stepwise pathways for dissociative electron transfer, [33][34][35] including the use of the electrochemical transfer coefficient (α) as a tool to detect the transition between both pathways. 36 The electrochemical reduction of several polychloroacetamides was studied by Constentin et al 37 on glassy carbon electrode in dimethylformamide by cyclic voltammetry. The authors found that electrochemical reduction of polychloroacetamides leads to their complete dechlorination in successive and separated steps, each one corresponding to the cleavage of one C-Cl bond in a two electron process.…”