Simultaneous electron transfers

Thus 2-ketoquinuclidine 25 gives quinuclidine in good yields [120]. There is no overlap between the a-bond and the carbonyl 7i -orbital to assist simultaneous electron transfer and bond cleavage. 

At equilibrium (i.e., no current) there exist dynamic currents, measured in amps, at each electrode and are a fundamental characteristic of electrode behavior. The anode and cathode exchange current densities can be defined as the rate of oxidation and reduction respectively. The exchange current density is a measure of the electrode s ability to transfer electrons and occurs equally in both directions resulting in no net change in composition of the electrode.22 A large exchange current density represents an electrode with fast kinetics where there is a lot of simultaneous electron transfer. A small exchange current density has slow kinetics and the electron transfer rate is less. 

We demonstrated further that in the coupling reactions, H- gives electrons to benzyl bromide, leading to benzyl anions). This step of the reaction is generally symbolysed by a simultaneous electrons transfer. Of course it must be understood as pictured in Scheme 2. 

The differences in selectivity between catalysts cannot be explained only in terms of the strength of reactant adsorption. A tentative explanation lies in the preference of platinum for concerted addition of protons to adsorbed alkenes with simultaneous electron transfer (25). The electronic structure of the surface intermediate of the concerted step appears to lead to halide cleavage. Palladium, on the other hand, can participate in insertion reactions (305) and promotes surface reaction between hydrogen atoms and adsorbed alkenes 4Sa. It is possible that palladium adsorbs vinyl halides on two different sites or at two different states, dependent on potential, one of which... 

The distribution of deuteroethylenes and deuteroethanes suggested that the opening step, reaction (90), should be a concerted reaction between adsorbed ethylene and hydrogen ions in solution with simultaneous electron transfer. The same experimental results indicated that the second step involved preferentially surface species, reactions (92) and (93), and not H in... 

The rates of reaction for O2 with RCCI3 compounds are proportional to their reduction potentials, which is consistent with the SET mechanism. A plot of log fci / [S] (Table 7-1) against the reduction potentials of RCCI3 compounds is approximately linear with a slope of -4.9 decade per volt. Such behavior is consistent with a mechanism that occurs via simultaneous electron transfer and nuclear motion. This correlation indicates that in water, where the 02/02 redox potential is about 0.44 V more positive, the rate of the reaction for 02 with CCI4 would be about 100-200 times slower than in aprotic solvents. 

Fig. 7.31 Results calculated for simultaneous electron transfer from the conduction band and surface states to an oxidizing agent in solution, for electron transfer processes from the conduction band (rate constant k c = lO cm s" ) and from the surface states (k y, a) and c) current normalized to equal intensities b) Fermi function describing the occupation of surface states c) as a) but with /Cs = 0 (compare with Fig. 7.30. The parameters are different light intensities varying...

Arylalkanes can react with electrophihc oxidants [58] to produce alkyl radicals via simultaneous electron transfer and deprotonation ... 

On Pt-based electrocatalysts, some evidences suggest that the first electron transfer composed of O2 adsorption with simultaneous electron transfer and proton addition is the rate determining step at the overall reaction processes. This may be represented by [7]... 

Fig. 8 Adiabatic free energy surface for simultaneous electron transfer and bond breaking from MD simulations (upper) and a linear response solvent model (lower panel) [36],...

In TBAH/AN solution, the dendrimer showed a single reversible redox wave at +0.82 V versus Fc/Fc+ corresponding to the Fe(II/III) process, indicating simultaneous electron transfer at the same potential. Unlike the other dendrimers in the same generation as mentioned above, deposition onto the electrode was not evident in this case. 

The mechanism for this reaction is not of the Langmuir-Hinshelwood form, but rather involves the reaction between a surface-bonded NO molecule with an NO molecule in the solution phase along with a simultaneous electron transfer. The Tafel slope in acidic solution is (120 mV), which implies that the first electron-transfer step is rate-determining (see Addendum to this chapter). The reaction is first order in H+ and shows no apparent isotope effect. The following mechanism has been proposed ... 

Spectral change of the cathode active material during discharge of the LIB can be explained by intercalation or sorption of Li" " and simultaneous electron transfer from the anode to the cathode, that is,... 

Campbell, J.L. Hager, J.W. Le Blanc, J.C.Y. On Performing Simultaneous Electron Transfer Dissociation and Collision-Induced Dissociation on Multiply... 

An elementary act of a traditional homogeneous redox reaction can be considered as a collision of the reacting particles with a simultaneous electron transfer from the reductant to the oxidant. This approach does not work with electrochemical processes. Here, the reactant and the oxidant are separated in space and the electron transfer occurs through the external circuit. Thus, an electrochemical reaction is accompanied by electron flow. The directed electron flow might be induced by a spontaneous reaction in the circuit. In this case, one deals with a Galvanic cell. On the craitrary, in an electrolytic cell, the electric current from an external source may cause non-spontaneous chemical transformations. 

The attempts of Bryce [21] to make aryl ester dendrimers decorated with external tetrathiofulvalene (TTF) revolved around the same approach as that of Miller and Neenan. Bryce et al. [21] started from a phenol containing two ester TTF moieties and used 5-tert-butyldimethylsilylisophthalic chloride as the building block. 1,3,5-Benzene tricarbonyl chloride was taken as the central core to couple second-generation dendrons. The second-generation dendrimer aryl ester dendrimers fitted with 12 terminal TTF units were then oxidized. Investigation of their redox behavior showed that simultaneous electron transfer did occur. 

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