Dissociative electron transfer intramolecular

Intramolecular dissociative electron transfer 146 Homolytic cleavage 152... 

Note, however, that the concerted/stepwise dichotomy discussed here concerns cases in which the intermediate is unstable toward cleavage that occurs by means of intramolecular dissociative electron transfer. As discussed in the foregoing sections, for primary radicals that cleave homolytically, criteria based on the life-time of the intermediate may be pertinent. 

Carbonyl compounds are also suited to the investigation of the role of solvent reorganization in the dynamics of intramolecular dissociative electron transfer as observed in a series of phenacyl derivatives bearing various leaving groups.199... 

In the case of stepwise processes, the cleavage of the primary radical intermediate (often an ion radical) may be viewed in a number of cases as an intramolecular dissociative electron transfer. An extension of the dissociative electron transfer theory gives access to the dynamics of the cleavage of a primary radical into a secondary radical and a charged or neutral leaving group. The theory applies to the reverse reaction (i.e., the coupling of a radical with a nucleophile), which is the key step of the vast family of... 

Morse Curve Model of Intramolecular Dissociative Electron Transfer... 

The classical Morse curve model of intramolecular dissociative electron transfer, leading to equations (3.23) to (3.27), involves the following free energy surfaces for the reactant (Grx-) and product (Gr +x ) systems, respectively ... 

In the stepwise case, the intermediate ion radical cleaves in a second step. Adaptation of the Morse curve model to the dynamics of ion radical cleavages, viewed as intramolecular dissociative electron transfers. Besides the prediction of the cleavage rate constants, this adaptation opens the possibility of predicting the rate constants for the reverse reaction (i.e., the reaction of radicals with nucleophiles). The latter is the key step of SrnI chemistry, in which electrons (e.g., electrons from an electrode) may be used as catalysts of a chemical reaction. A final section of the chapter deals... 

Intramolecular dissociative electron transfer in aryl halide radical-anions involves an interaction between the n-aroinatic orbital and the o-type carbon-halogen bond. These orbitals are orthogonal, but bending of the carbon-halogen bond allows the necessary interaction. Qualitatively, the influence of several factors on the bond cleavage rate can be discerned [18],... 

Inner-sphere. Here, the two reactants first form a bridged complex (precursor)- intramolecular electron transfer then yields the successor which in turn dissociates to give the products. The first demonstration of this was provided by H. Taube. He examined the oxidation of ICrfHoOijj by lCoCl(NHr)< and postulated that it occurs as follows ... 

There are no large differences between the reactivities of PhS , (EtO)2PO and CHjCOCHj" with the same aryl radical, but CN appears to be significantly less reactive. It is not easy to evaluate the respective role of the bond dissociation free energy and of the Nu-/Nu" standard potential in equation (13) in this connection because of the paucity of available data concerning these two quantities. An explanation of the low reactivity of CN" should thus await the availability of such data as well as that of a precise expression of the intrinsic barrier in a model of these intramolecular concerted electron-transfer-bond-breaking (or forming) reactions. 

Of course the Co CNHj) breaks down rapidly in acid into Co + and 5NHJ. Precursor complex formation, intramolecular electron transfer, or successor complex dissociation may severally be rate limiting. The associated reaction profiles are shown in Fig. 5.1. A variety of rate laws can arise from different rate-determining steps. A second-order rate law is common, but the second-order rate constant is probably composite. For example, (Fig. 5.1 (b)) if the observed redox rate constant is less than the substitution rate constant, as it is for many reactions of Cr +, Eu +, Cu+, Fe + and other ions, and if little precursor complex is formed, then = k k2kz ). In addition, the breakdown of the successor complex would have to be rapid k > k 2). This situation may even give rise to negative (= A//° +... 

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