Subject electron-exchange reactions

Thus the Marcus theory gives rise to a free energy relationship of a type similar to those commonly used in physical organic chemistry. It can be transformed into other relationships (see below) which can easily be subjected to experimental tests. Foremost among these are the remarkably simple relationships that were developed (Marcus, 1963) for what have been denoted cross reactions. All non-bonded electron-transfer processes between two different species can actually be formulated as cross reactions of two self-exchange reactions. Thus the cross reaction of (59) and (60) is (61), and, neglecting a small electrostatic effect, the relationship between kn, k22 and kl2... 

To sum up the survey of the past work on oxidation-reduction reactions the only experimental results obtained thus far which strongly indicate nonadiabatic effects are some obtained by Matteson and Bailey (22) and by Chan and Wahl (23) for self-exchange reactions. In addition, it is very likely that such effects are significant also for reactions of f electron redox agents, particularly on reaction with one another. Marcus has advocated consistently the position that nonadiabatic effects are relatively unimportant for the ordinary oxidation—reduction reactions which have been studied. But many experimentalists, including myself, have been much slower to arrive at it. Further work may show that a nonadiabatic factor is significant in many other processes, but at the present level of development of the subject, there are not many cases where it needs to be invoked. 

Layered compounds provide unique character for electron-transfer processes owing to their low dimensionality. Especially layered materials with ion-exchange and/or intercalation capabilities show behavior that is not seen in so-called bulk-type materials. Layered materials, which have been often used in studies of photoelectron transfer as well as photocatalysis, may be classified into two groups compounds in which the host layers work as an active component for the photoexcitation and electron-transfer reactions, and materials in which the layers are inert for electron-transfer processes. Examples of the former are layered titanates and niobates and of the latter are clays. In the latter case, photoactive materials are intercalated in the interlayer spaces. Recently, the exfoliation of various layered compounds has become possible and artificial assemblies consisting of these exfoliated sheets have been formed. Electron transfer in such assemblies is also an attractive subject in this field. 

The remainder of this section will focus on true SBMs, which have been the subject of vigorous research. Despite the electron deficiency of early transition metal, lanthanide, and actinide complexes, several groups reported that some of these d f" complexes do react with the H-H bond from dihydrogen and C-H bonds from alkanes, alkenes, arenes, and alkynes in a type of exchange reaction shown in equation 11.32. So many examples of SBM involving early, middle, and late transition metal complexes have appeared in the chemical literature over the past 20 years that chemists now consider this reaction to be another fundamental type of organometallic transformation along with oxidative addition, reductive elimination, and others that we have already discussed. 

Permanganate oxidation of organic compounds can occur via several different reaction pathways electron exchange, hydrogen atom abstraction and direct donation of oxygen [116]. The resulting pathway is subject to reaction conditions and the molecule reacting. 

Most redox proteins contain a redox-active group that is partially or completely buried inside their polypeptide backbones. Clearly, this design is meant to discriminate between possible electron-transfer partners, in such a way that only those approaching the protein at the right locations will be allowed to exchange electrons with the redox functional group. Therefore, the electron-transfer reactions of encapsulated redox centers are the subject of considerable current interest. Most groups... 

It is clear that the oxygen reduction reaction (ORR) is one of the most important electrochemical reactions since it has multiple applications. The potential fields range from the energy conversion to corrosion science. For this reason, it has been the subject of numerous works throughout the years. In the complete reduction of oxygen to water, there are four electrons exchanged. This high number of electrons... 

Electron-transfer reactions are amongst the most important processes in electrochemistry. Indeed, all electrochemical reactions involve an exchange of electrons between a particle and the electrode at some stage. Therefore, electron transfer has been the subject of intensive research ever since the rise of electrochemical kinetics toward the middle of the last century. 

In experimental studies of photoinduced electron transfer reactions, the free energy dependence of the quenching of a particular metal complex (e.g, Ru(bpy)3 + ) by a series of structurally related quenchers of known properties is used to confirm the calculated potential of the excited state couple and to estimate its exchange rate. For a given quencher a graded series of polypyridine complexes with different substituted bpy/phen ligands can also be used equivalently. These provide a set of experimentally measured data to check the observation of normal and inverted behaviour predicted by Marcus theory under certain conditions. Rate constants for back electron transfer of photoredox products have been measured in a similar manner in some cases and these were also subjected to analysis. 

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