Electron transfer homogeneous

Electron transfer reactions involving alkali metals are heterogeneous, and for many purposes it is desirable to deal with a homogeneous electron transfer system. It was noticed by Scott39 that sodium and other alkali metals react rapidly with aromatic hydrocarbons like diphenyl, naphthalene, anthracene, etc., giving intensely colored complexes of a 1 to 1 ratio of sodium to hydro-... 

Theories of Elementary Homogeneous Electron-Transfer Reactions Sacher, E. Laidler, K. J. 3... 

Mainly, three approaches have been used to immobilize the enzyme on transducer or electrode surface, single layer, bilayer, and sandwich configurations [69, 98], In some studies enzymes are covalently linked with sol-gel thin films [99], Sol-gel thin films are highly convenient for fast, large, and homogeneous electron transfer [17]. With an increase in gel thickness the signal decays and diffusion of analytes to biomolecule active site becomes difficult eventually these factors lead to poor response. By employing thin films various biosensors such as optical and electrochemical biosensors have been reported. 

Another interesting case concerns a homogeneous electron transfer reaction, namely, the initiation step of the classical Kornblum-Russell reaction153155 of 2-nitropropanate ions with 4-nitrobenzyl chloride (Scheme 14). 

Electron-transfer reactions at ITIES resemble electron-transfer reactions across biological membranes, which adds a special interest. Also, in contrast to homogeneous electron-transfer reactions, they allow a separation of the reaction products. So it is disappointing to report that only very few experimental investigations of electron-transfer reactions at ITIES have been performed. This is mainly due to the fact that it is difficult to find systems where the reactants do not cross the interface after the reaction in addition, side reactions with the supporting electrolyte can be a problem. 

Here, i is the faradaic current, n is the number of electrons transferred per molecule, F is the Faraday constant, A is the electrode surface area, k is the rate constant, and Cr is the bulk concentration of the reactant in units of mol cm-3. In general, the rate constant depends on the applied potential, and an important parameter is ke, the standard rate constant (more typically designated as k°), which is the forward rate constant when the applied potential equals the formal potential. Since there is zero driving force at the formal potential, the standard rate constant is analogous to the self-exchange rate constant of a homogeneous electron-transfer reaction. 

Homogeneous electron transfer between an electron donor and an electron acceptor,... 

It should be noted that the conditions that make possible the occurrence of an ECE mechanism, involving the reduction of C at the electrode surface, involve the possibility of another mechanism in which the second electron is transferred from B to C rather than from the electrode as pictured in Scheme 2.5. This homogeneous electron transfer reaction may be viewed as a disproportionation reaction insofar that A has one oxidation number more than B and C, and D, one oxidation number less. 

Homogeneous Electron Transfer as the Rate-Determining Step The... 

FIGURE 2.1 7. Homogeneous catalysis electrochemical reactions. Kinetic zone diagram in the case where the homogeneous electron transfer step is rate limiting. 

FIGURE 2.18. Homogeneous catalysis electrochemical reactions with the homogeneous electron transfer as a rate-limiting step. Typical dimensionless current-potential curves, a From bottom to top, logAe — —1.5, —1, —0.5, 0, 0.5, 1. b from bottom to top, logAe — 2, -0.5, -1, -1.5. 

When k eCp/kc <1, the rate-determining step is the forward homogeneous electron transfer reaction, meaning that the system behaves as just analyzed above. When, conversely, k ed /kc 1, the rate-determining step is the follow-up reaction, while the homogeneous electron transfer plays the role of a preequilibrium. The governing kinetic parameter is then... 

Two-Electron Catalytic Reactions In a number of circumstances, the intermediate C formed upon transformation of the transient species B is easily reduced (for a reductive process, and vice versa for an oxidative process) by the active form of the mediator, Q. This mechanism is the exact counterpart of the ECE mechanism (Section 2.2.2) changing electron transfers at the electrode into homogeneous electron transfers from Q, as depicted in Scheme 2.9. In most practical circumstances both intermediates B and C obey the steady-state approximation. It follows that the current is equal to what it would be for the corresponding EC mechanism with a... 

Back electron transfer is at the diffusion limit because the homogeneous electron transfer reaction is uphill, owing to the fact that the standard potential of the redox catalyst is necessarily chosen as positive of the reduction potential of the substrate. 

In the case of a homogeneous electron transfer between two molecules,... 

The situation where the radical-substrate coupling is a preequilibrium to the homogeneous electron transfer step, termed the rsdDISP2 mechanism, prevails when ).-d 3> /d)b. Then equation (6.56) becomes... 

We first consider the case where the rate-determining step is the forward homogeneous electron transfer step (rate constant ke). The governing equations are... 

Some Comparisons Between the Energetics of Electrochemical and Homogeneous Electron-Transfer Reactions... 

Similar to homogeneous electron-transfer processes, one can consider the observed electrochemical rate constant, k, , to be related to the electrochemical free energy of reorganization for the elementary electron-transfer step, AG, by... 

The theory of homogeneous electron transfer processes, as well as of the closely-related electron exchanges with metallic electrodes, has been the subject of considerable study. The proposal by Hush and by Marcus that these processes are, for simple systems, either usually electronically adiabatic or... 

The theory of homogeneous electron transfer reactions in solution has been formulated in terms of models in which the transferring electron is localized at a donor site in the reactant and at an acceptor site in the... 

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