Electron-transfer processes factors influencing reaction

Problems associated with precursor formation and successor dissociation are circumvented when the nonspecific interaction between donor and acceptor in Eq. 1, represented by, is replaced by a covalent linker. As the many chapters of this Series attest, the restriction of electron transfer to an intramolecular process, where the distance between donor and acceptor is fixed, has led, in the past two decades, to an explosion in our knowledge of electron transfer processes and the factors that control them. These include the donor-acceptor separation distance the nature of the intervening medium and the relative orientation between the donor and acceptor sites (all of which influence electronic coupling) the driving force of the reaction (AG°) and the nuclear reorganization of reactants and solvent (2). 

Despite the fact that electron transfer reactions at the electrode/electrolyte interface are of fundamental importance to many chemical processes, a quantitative understanding of the factors that influence the rate of these reactions is still lacking. Although the general theoretical framework was established many years ago by Marcus, Levich, Dogonadze, and oth-... 

Since not only the electron-transfer step but also adsorption and some of the chemical steps involved in an electrode reaction take place in the layer, the whole process should be strongly influenced by polar factors. The orientation of polar-adsorbed species, such as ion-radicals in particular, is electrostatically influenced, and consequently, the stereochemistry of their reactions is also controlled by such kind of electrostatic factor. All these phenomena have been summarized in several monographs. The collective volume edited by Baizer and Lund (1983) is devoted to organic electrochemistry. This issue is closer to the scope of our consideration than its latest version edited by Lund and Hammerich (2001) (these editors have changed the invited authors and, consequently, the chapters included). 

A key aspect of metal oxides is that they possess multiple functional properties acid-base, electron transfer and transport, chemisorption by a and 7i-bonding of hydrocarbons, O-insertion and H-abstraction, etc. This multi-functionality allows them to catalyze complex selective multistep transformations of hydrocarbons, as well as other catalytic reactions (NO,c conversion, for example). The control of the catalyst multi-functionality requires the ability to control not only the nanostructure, e.g. the nano-scale environment around the active site, " but also the nano-architecture, e.g. the 3D spatial organization of nano-entities. The active site is not the only relevant aspect for catalysis. The local area around the active site orients or assists the coordination of the reactants, and may induce sterical constrains on the transition state, and influences short-range transport (nano-scale level). Therefore, it plays a critical role in determining the reactivity and selectivity in multiple pathways of transformation. In addition, there are indications pointing out that the dynamics of adsorbed species, e.g. their mobility during the catalytic processes which is also an important factor determining the catalytic performances in complex surface reaction, " is influenced by the nanoarchitecture. 

The influence of the electron transfer resistor Ret and the slow process admittance Ysp on the total faradaic impedance is determined by which factor is reaction rate—limiting. It is possible to study this by plotting the faradaic impedance as a function of frequency in a log—log plot, or in the Wessel diagram and look for circular arcs (see Section 9.2). 

To understand the danger in proposing which reactions takes place to provide the required ES current on the basis of the standard electrode potentials alone, one must consider that several other factors influence the actual rate of a specific reaction. Assuming that mass transport is not the limiting factor, other processes such as the electron transfer rate at the electrode surface, chemical reactions preceding the electron transfer, or chemical... 

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