Problems and Prospects of the Concerted Dissociative Electron Transfer Mechanism.

A quantum mechanics-molecular mechanics study of dissociative electron transfer: The methylchloride radical anion in aqueous solution

“…in solution, these values being in good agreement with the degree of charge transfer observed for these complexes in argon matrix. 4,[10][11][12] Figure 4 shows the water hydrogens-chlorine atom radial distribution functions ͑RDF͒. In the case of the neutral molecule, the solutesolvent interaction is not enough to give a well-defined solvation shell around the chlorine atom.…”

“…9 This effect of the hydrogen bonds could also be related to the fact that dissociation rates are generally higher in dipolar aprotic solvents than in water. 4,8 …”

“…Electron attachment to these molecules leads to the formation of temporary radical anions which decay with lifetimes usually varying between 10 Ϫ13 and 10 Ϫ15 s. 1,2 One of the most typical examples of this kind of reactions is the electrochemical dissociation of alkyl and aryl halides RX ͑where XϭF, Cl, Br, I͒, which is a powerful technique for the production of alkyl and aryl radicals. 3 These reactions can be classified into two categories: consecutive or concerted dissociative reactions, 4 depending on the particular reaction mechanism followed ͑1 or 2͒:…”

“…8 Thus, for 4-nitrobenzylchloride, the rate constant increases in a factor of 10 2 when changing the solvent from water to dimethylformamide. 4 There is also some evidence of solvent-induced change from consecutive to concerted reaction mechanisms. 9 The radical anions of organic halides can also be generated by ␥ irradiation in lowtemperature matrices of inert solvents and studied by means of EPR spectroscopy.…”

“…4 Solvent effects have been considered in some studies, usually by means of continuum models. 13,17,18 In solution, the radical anion species is largely stabilized relatively to the neutral molecule, the dissociation process being clearly favored.…”