Oxidation potentials definition

Five oxidation states of At have been definitely established (-1, 0, +1, V, VII) and one other (III) has been postulated. The standard oxidation potentials connecting these states in 0.1 M acid solution are E°fV) ... 

It is known that the oxidation potentials of diazodiphenylmethane and Cu(I) in acetonitrile are very similar. With CuBr2 however, no radical-chain reaction takes place. Contrary to the copper perchlorates, CuBr2 and CuBr initiate identical reaction pathways involving copper carbenoids. No definite answer to this discrepancy is available 402). 

The role of biomass in the natural carbon cycle is not well understood, and in the light of predictions of a future atmospheric energy balance crisis caused by carbon dioxide accumulation, in turn the result of an exponential increase in the consumption of carbon fuel, the apparent lack of concern by scientists and policy makers is most troubling. Yet there is no other single issue before us in energy supply which will require action long before the worst effects of excess production will be apparent. The only satisfactory model is the action taken by the R D community with respect to the SST in nitric oxide potential and chloro-halocarbon emissions, when it was realised that the stratospheric ozone layer was vulnerable to interference. Almost all other responses to pollution" have been after definitive effects have become apparent. 

The Pi parameter can be obtained in less direct (but often more convenient) ways than that corresponding to the immediate use of Eq. (4) (its definition expression) that requires the synthesis of the corresponding ]Cr(CO)5L] complex (which in many cases may even be unknown) and the measuring of its oxidation potential. In fact, if one knows... 

Review work for future updates of our data base should focus on iron compounds and complexes. The iron system is thought to be of crucial importance for characterizing the redox behaviour of radioactive waste repositories. Preliminary applications have indicated that the lack of data for the iron system is a source of major uncertainties associated with the definition of an oxidation potential. Hence, there is little use in developing sophisticated redox models for radionuclides as long as the dominant redox processes in a repository are poorly known. 

The loss of an electron by M, M + + e, is the process of oxidation in electrochemistry. The electron is then accepted by an electrode of well defined potential, so that the oxidation potential Eox is the free energy of the reaction, as was seen in Figure 4.1. Similarly the reduction potential Ered is the energy of the reduction reaction, e.g. N + e - N. By definition the molecule, which is oxidized, is the donor (M in this case), and the molecule, which is reduced, is the acceptor. The electron transfer from M to N is therefore equivalent to the combined oxidation of the donor and reduction of the acceptor, so that the energy balance is... 

All molecules with nonbonding electron pairs (e.g., H20, / OH, ROR, / NH2, / SH, RSR) are, by definition, Lewis bases with a degree of nucleophilicity. Their electrochemical oxidation potential is a measure of (1) the ease of removal for one of the electron pair of electrons and (2) relative nucleophilicity (the less positive the potential, the more nucleophilic). Aromatic molecules with Lewis base substituents are easier to oxidize than the aliphatic forms of the substituents (e.g., PhOMe, +1.75 V vs. SCE MeOH, +2.5 V vs. SCE) because the aromatic ring provides a means for delocalizing the positive chaige and electron spin that would result from electron removal (in the case of PhOMe, there are five additional hydrogen atoms to share the positive chaige and six... 

The oxidation potentials in Table 9, which refer to aqueous Ag/AgCl/KCl (sat.) electrodes, correspond well to the data in Tables 5-8. However, as mentioned in the introductory section, the definition of the oxidation potentials of nonaqueous systems may be very vague in many cases and may thus depend on subjective definitions (such as significant anodic currents ). 

In this connection, it is essential to discuss the reduction potentials E of oxygen derived reactive species and of several other intermediates that are important in AOPs (Tab. 6-1). For a viable definition of the term reduction potential , which should be used instead of the obsolete oxidation potential or of the ambiguous redox potential the reader is referred to Wardman s (1989) comprehensive review and data collection. The reduction potentials E of couples M/M refer to reactions described by Eq. 6-1 or Eq. 6-2. 

Because of thermodynamic and electrochemical conventions, standard potentials are defined in the direction of reduction, independently of the respective chemical stabilities of the molecules involved. Thus for the oxidation of toluene to its cation radical, E° refers to the reduction of the highly unstable cation radical into the highly stable toluene. To overcome such a priori chemical nonsence, E is frequently designated as the standard oxidation potential of toluene for example. However, such a term should not be accepted according to canonical rules because it formally implies that the cell now operates in a driven mode, that is, is connected to an external power supply [19]. Thus in this chapter we prefer to use the denomination standard reduction potentials, rather than the usual temi standard potential, as a reminder of the E° definition, although such as expression is basically a pleonasm. 

An electrode potential is, by definition, a reduction potential. An oxidation potential is the potential for the half-reaction written in the opposite way. The sign of an oxidation potential is. therefore, opposite that of a reduction potential, but the magnitude is the same. 

It was soon realized, however, that this simple definition of nucleophilicity would not suffice. Shortly afterward, Edwards (6) attempted to define relative nucleophilicities in terms of two parameters, H (basicity) and Eox (oxidation potential), using the (variable) coefficients a and to relate these properties to changes in the electrophile (equation 5). Later, Edwards and Pearson substituted a polarizibility parameter, P, for Eox. In essence, equation 5 is a Brpnsted equation with a second parameter added. 

The oxidation potential of the 2 SCN = (SCN)2 couple Mis between those of the corresponding couples for Br and 1 (Table II) (38-40). The SCN = OSCN couple is comparable to the corresponding 1 couple (41). The oxidation potential of SCN relative to the halides explains the oxidation of SCN by CI2 (42) and Br2 (43) and the oxidation of 1 by (SCN)2. The latter reaction is one that can be used to quantify (SCN)2 (44). The relative oxidation potentials also facilitate the definition of inter (pseudo)halogens like I -SCN (iodine thiocyanate) (45,46) versus Cl -SCN (thiocyanogen chloride) (47) and Br -SCN (thiocyanogen bromide), which react accordingly. 

The fields marked Fe203 and Fe304 are sometimes labeled passivation on the assumption that iron reacts in these regions to form protective oxide films. This is correct only insofar as passivity is accounted for by a diffusion-barrier oxide layer (Definition 2, Section 6.1). Actually, the Flade potential, above which passivity of iron is observed in media such as sulfuric or nitric acid, parallels line a and b, intersecting 0.6 V at pH = 0. For this reason, the passive film (Definition 1, Section 6.1) may not be any of the equilibrium stoichiometric iron oxides, as is further discussed in Chapter 6. 

Voltammetric measurements are done by applying a potential scan to the working electrode. When the potential reaches the range where the analyte will be either reduced or oxidized, a definite electrical current starts to flow. When the current is measured at a constant potential the technique is called... 

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