Three-electron process

In fact, this molecule displays a single three-electron process characterized by chemical reversibility (even if slight adsorption phenomena make the reverse peak slightly higher than the forward peak). 

Figure 41 shows that in acid solution this tetracation undergoes a first reversible oxidation RuIIIRuIII/RuIIIRuIV (E0 = +0.79 V), followed by a second three-electron process (E° = +1.22 V). 

Oxidation Processes. Because of the presence of several metal ions, each capable of undergoing an oxidation process, our polynuclear compounds show complex, very interesting oxidation patterns. For tetranuclear complexes like and 4B (Scheme 1 and Table 1) a 3-1 oxidation pattern is expected, i.e., a three-electron process related to the oxidation at the same potential of the three peripheral, equivalent, and noninteracting RuL2(p-2,3-dpp) units followed by a one-electron process related to the oxidation of the central Ru(p-2,3-dpp)3 component. The experimental results, however, support only the first process (Table 2) because the presence of the three contiguous, already oxidized peripheral components displaces the oxidation of the central metal ion at potentials more positive, practically outside the accessible potential window. 

D. The chronoamperometric results can also be used to ascertain the number of electrons involved in the formation of benzonitrile from p-chloro-benzonitrile. In order to translate the chronoamperometric data into a meaningful n value, a compound is selected that has a diffusion coefficient very similar to that of p-chlorobenzonitrile and that gives a stable, known product upon electroreduction. Tolunitrile, which satisfies these criteria, is known to be reduced to its radical anion at a diffusion-controlled rate. Since this one-electron process gives a value of 168 pA s1/2- M x cm 2 for it1/2/CA, the corresponding value of 480 pA s1/2 A/ 1 cm-2 for the reduction of p-chlorobenzonitrile to benzonitrile anion radical must represent an overall three-electron process. When we subtract the one electron that is required to reduce benzonitrile to its radical anion from this total, we immediately conclude that two electrons are involved in cleavage of the carbon-chlorine bond in p-chlorobenzonitrile. A scheme that is consistent with these data is described by Equations 21.1 to 21.6. 

The half-cell reaction of the reduction of permanganate is a three-electron process ... 

Nitric acid HN03 The oxidizing action of nitric acid depends on the concentration of the acid and the temperature of the solution. Normally, nitrogen oxide is formed in a three-electron process ... 

The chemistry of hydrogen depends mainly on three electronic processes ... 

Figure 18 The Auger electron emission process is a three-electron process involving both core and valence-level electrons...

Also in this case, the occurrence of a single-step three-electron process indicated that the three ferrocenyl ligands, from which the electrons are concomitantly removed, are non-communicating. In addition, if one considers that, under the same experimental conditions, ferrocene undergoes oxidation at E° = 4-0.45 V, it is evident that the ferrocenyl ligands are only slightly electronically perturbed by complex formation with the CpTi fragment. 

In organic chemistry electrons are, as a rule, transferred one by one [7]. This is in contrast to inorganic electron transfer reactions, where two- and three-electron processes are common. However, in order to preserve the formalism generally used in electrochemistry, the number of electrons n is maintained in most formulas, although n equals one in practically all cases. 

At — 30°C, reduction of the triazine ligand is not observed. Instead, full reduction of the clusters via a three-electron process occurs, and no exchange intensity is apparent. This is likely due to restriction of rotation about the cluster-triazine bonds, resulting in unfavourable orbital overlap at low temperature. 

In aqueous alkaline solutions containing 0.1 to 1.0 VI alkaline hydroxide, the polar-ograms revealed four waves. The first wave at E, 2 -0 8 V I .v SCE exhibited an alternating eurrent efficiency of nearly 90% [21] and can be attributed to a two-electron change [14, 21, 22], The second wave at 1/2 = -1.1 V was found to be well separated from the first wave and corresponded to a three-electron process of low reversibility. 

ESCA is especially useful in the analysis of organic materials. Furthermore, chemical shift of the core levels enables conclusions on the binding to be more easily drawn for this one-electron process than for the complicated three-electron process of AES. When excitation is performed with ultraviolet light in the range of 4 to 40 eV (UPS) instead of X-rays of 1200 to 1500 eV, only weakly bound valence-shell electrons react. Such electron spectra are sensitive to molecular orbital effects and are used for their investigation, but they do not possess elemental significance. 

The question of the adiabacity of the [Co(NH3)6] self-exchange reaction has continued to be discussed. This self-exchange reaction is formally spin-allowed, but since it is a three-electron process it is orbitally forbidden. Newton has used an ab-initio, SCF approach to treat the ( Aig)[Co(NH3)6] -C rig)[Co(NH3)6] self-exchange, and he has found that spin-orbit coupling and... 

The [Co ] /[Co(sep)] " reactions are formally three-electron processes, similar to those discussed above, while the [Co ] " /[Ru(NH3)6] reactions are two-electron processes. The magnetic field and IPCT perturbation studies indicate that ei < 1 for both of these classes of electron transfer reaction, but smallest for the former. For a given coordination environment, outer-sphere electron transfer reactions involving cobalt(III) and high-spin cobalt(II) couples are likely to result in smaller values of than most other transition metal, one-electron transfer couples. 

It is frequent that electroactive molecules exchange more than one electron in successive transfer steps, giving rise to multi-E mechanisms. This situation is commonly found in the electrochemistry of organic and organometal-lic compounds [3] and biological molecules [11], In order to show how to tackle this problem, we consider a three-electron process involving four electroactive species, although the same treatment is applicable to any number of consecutive electrochemical processes ... 

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