Electron transfer theory examples

In the electron transfer theories discussed so far, the metal has been treated as a structureless donor or acceptor of electrons—its electronic structure has not been considered. Mathematically, this view is expressed in the wide band approximation, in which A is considered as independent of the electronic energy e. For the. sp-metals, which near the Fermi level have just a wide, stmctureless band composed of. s- and p-states, this approximation is justified. However, these metals are generally bad catalysts for example, the hydrogen oxidation reaction proceeds very slowly on all. sp-metals, but rapidly on transition metals such as platinum and palladium [Trasatti, 1977]. Therefore, a theory of electrocatalysis must abandon the wide band approximation, and take account of the details of the electronic structure of the metal near the Fermi level [Santos and Schmickler, 2007a, b, c Santos and Schmickler, 2006]. 

We have established an important principle in electron transfer theory that is not present in conventional one-dimensional models. The reaction coordinate is always localizing and corresponds to coordinate Aj. The coordinate X2 corresponds to the direction in which the matrix element between ground and excited states is switched on. If this coordinate has zero length then the branching space becomes one dimensional and an adiabatic reaction path does not exist. We now consider two examples. 

Kavamos GJ, Turro NJ (1986) Photosensitization by reversible electron transfer theories, experimental evidence, and examples. Chem Rev 86 401 -49... 

We believe that these few examples add to the others cited in this chapter to demonstrate that the standard formalism of electron transfer theories is well adapted to the interpretation of biological processes. The numerous investigations based on this formalism which are presently developed may be divided into two categories ... 

Supramolecular chemistry has provided an experimental platform for testing many modern theories on bonding, molecular organization, photochemistry, and in particular, electron transfer theory. For example, in 1956, Marcus predicted that highly exoergonic electron transfer reactions actually slow down with increasing driving force. Numerous bimolecular electron transfer reactions were studied... 

One particular example of the use of pulse radiolysis to general chemistry was the work of Miller and co-workers on the rates of electron-transfer reactions. These studies, which were begun using reactants captured in glasses, were able to show the distance dependence of the reaction of the electron with electron acceptors. Further work, where molecular frameworks were able to fix the distance between electron donors and acceptors, showed the dependence of electron-transfer rate on the energetics of the reaction. These studies were the first experimental confirmation of the electron transfer theory of Marcus. 

Kavarnos, G.J., TUrro, N.J. (1986), Photosensitization by Reversible Electron Transfer Theories, Experimental Evidence, and Examples," Chem. Rev. 86, 401. 

The purpose of this section is not to present a compendium or a discussion of the numerous experimental illustrations of the validity of electron transfer theories, but rather to select two typical examples that illustrate the main features of these theories in organic chemistry [63]. 

The calculations presented here show that many different factors must be considered in estimating the rate constant. Nevertheless, electron transfer theory is remarkably successful in describing this elementary solution reaction. Theory has gone much further than described here, especially in developing the quantum-mechanical description of electron transfer. More details can be found in recent reviews [29, 30]. There are other related topics which have not been discussed in this section. They include, for example, photo-induced electron transfer [30], and the Marcus cross-relation [5]. 

In this chapter, we focus on the hopping regime and start with a primer on electron-transfer theory in Section 1.1.2. This section will underline the three major parameters that enter the expression of the electron-transfer rate reorganization energy, electronic coupling, and driving force. We then discuss some examples of the impact of chemical structure and packing mode on these parameters. Section... 

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