Direction of electron transfer

This system illustrates the importance of both the thermodynamic and intrinsic barriers in determining the direction of electron transfer within a given reactant pair. In addition, systems such as the one considered here in which the oxidative and reductive pathways possess comparable rate constants afford an opportunity of controlling or switching the direction of electron transfer by modifying one of the barriers. 

For example, in the electron-transfer system shown in Figure 6.25 the protein-bound groups between which electron transfer occurs are designated A, B and C and the direction of electron transfer is shown as arrows. 

The direction of electron transfer in the exciplex, determined by the inequality... 

This is qualitatively illustrated by the data49 in Table XII which confirms the direction of electron transfer in these systems. 

Fig. 4, Correlations between electron transfer energy levels in metal electrode and in redox species. At equilibrium (Fy = °Fre for anodic (rja> 0) and cathodic (tjc<0) polarisation (Fy =°Fredox — e0 > ). The arrows indicate the direction of electron transfer...

The excess negative charge located in the interior of metallic silver colloids could also be transferred to other electron acceptors, including methylviologen, nitrobenzene, nitropyridinium oxide, anthracene quinone sulfonic add, and potassium cyanohexaferrate(III)[506, 531], The efficiency and, indeed, the direction of electron transfer were found to depend on the position of the Fermi level of the surface-modified silver particles. For example, chemisorption of AgN to a silver particle is shown to result in a shift of the Fermi level to a more positive potential, as shown in the lower line in Fig. 84. 

In the first case, M is the electron donor and N is the electron acceptor, these roles being reversed in the second case. These properties of donor and acceptor are relative, the same molecule M being a donor towards some species N and an acceptor towards other partners N. It will be seen presently that the direction of electron transfer depends simply on the energy balance of the reactions. 

Fig. 19. The scheme of bands explaining the voltage-current curve of a tunnel diode, a. The p-region b, the n-region c, the forbidden energy gap. Arrows show the directions of electron transfer. 0, The case of the zero shift of the Fermi levels 1, 2, tunneling through the forbidden energy gap 3, the position of bands corresponding to the minimum of the voltage current curve for a diode 4, thermal currents.

I Direction of vectorial proton translocation Direction of electron transfer... 

In electroorganic reactions, the active species is generated on the electrode surface by electron transfer between a substrate molecule and the electrode, as shown in equation (1). The substrate molecule is transformed to a cation radical or an anion radical, depending on the direction of electron transfer. When the substrate molecule is a radical or ionic species, the transformation of the substrate is as shown in equation (2). 

FIGURE 11. An escapement mechanism is sometimes used to control the direction of electron transfer within a redox cluster (small box). Here electron transfers from the substrate (close pair of circles filled with electrons) to a redox center on the left which is effectively insulated by distance from other members of a redox chain (further left) so only one electron can be transferred. The radical intermediate can transfer electrons to the chain on the right. The thermally activated escapement motion of the redox center then carries an electron to the chain at the left, and finally reassembles the cluster in preparation for the next catalysis. 

Figure 5.26 shows an LB film that regulates electron transfer. Monolayers of an electron donor layer, an insulating fatty acid layer and an electron acceptor layer were transferred in a defined sequence. In this hetero-layered LB film, electron transfer only occurs from the inside to the outside, and the structure of the insulator layer determines the efficiency of electron transfer. Swapping aroimd the donor layer and the acceptor layer reverses the direction of electron transfer. Simply controlling the layering structure therefore enables us to modulate the direction and efficiency of electron flow. 

Structure capable of forming the three covalent bonds. Thus the transfer of an electron from one atom to the other has produced, in addition to the Goulombic attraction between the ions, an additional covalent bond. Such bonds have from time to time been given special names, e,g. semi-polar, dative or coordinate, and have been represented in structure formulae by an arrow, viz G 0+ showing the direction of electron transfer. In view of the fact that such bonds utilize no new binding force, such names now appear unnecessary. 

A combination of optical kinetic measurements and oxygen electrode measurements serves to evaluate rate constants and indicate the direction of electron transfer, as well as confirming the overall stoichiometry of the reaction. 

The following mechanistic issues remain controversial (I) whether in the formation of EDA complexes it is the adsorbent or the adsorbate that acts as the electron donor (2) to what extent the molecular orbital theory, and the difference between the HOMO and LUMO levels of the adsorbate and the adsorbent, can predict the degree and the direction of electron transfer that leads to chemisorption. 

Use SpartanView to compare electrostatic potential maps of the ethyl cation, the isopropyl cation, and the ierf-butyl cation. How does the number of alkyl groups attached to the positive carbon change the potential at this atom What does this imply about the direction of electron transfer between an alkyl group and the positive carbon ... 

The transition state in a Diels-Alder reaction involves transfer of electrons from one molecule to the other. Using SpartanView to compare electrostatic potential maps of cyclopentadiene, tetracyanoethylcne, and their Diel.s-Alder transition state, describe the direction of electron transfer. 

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