Oxidation potential, Eox

The MS response after Sn(IV) addition is given in Fig. 4.5 for two oxidation potentials Eox. The C02 signal grows and passes through a maximum after some minutes. A more pronounced response is observed at higher potentials. The lowest potential at which this effect can be observed is ca. 0.425 V. Blank experiments (without addition of tin, dashed curve in Fig. 4.5) show a C02 production at potentials above 0.4 V, but this was always lower than in the presence of tin. 

Fig. 5 Global correlation of the oxidation potentials Eox (V versus SCE) with the vertical ionization potentials IP (eV) of various types of organic donors identified in Table 3.

Figure 20, Unified free energy relationship for ion-pair formation. Key left, free energy relationships between the rates of reaction (log kobJ and the oxidation potential Eox° of the donor and right, after inclusion of the work term following Equation 31, (Keys to symbols are located at the far left.)...

Extensive investigations of ECL processes have established a general, sometime quite complicated, scheme for ECL emission. In the electrochemical reactions, an electron acceptor A is reduced to A at the reduction potential Ercd and an electron donor is oxidized to D + at the oxidation potential Eox as follows ... 

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... 

Since the redox potentials of dye aggregates adsorbed onto platinum electrode exhibit a broad distribution centred at the formal oxidation potential Eox, the direct information on the ionization energy of the aggregated cyanines can be obtained, even in case of irreversibly oxidizing dyes, from the potential dependence of the fractional degree of dye oxidation, 0, derived from the potential-step electrochemical measurements [52, 53]. The analogue of Nemst equation describing the oxidation process can be written as ... 

Bordwell (Bordwell and Bausch, 1986) has developed a method to determine C—H BDEs from a combination of pXHA values and oxidation potentials (Eox) of the corresponding anions in dimethyl sulphoxide solution. These acidity-oxidation potentials (AOP) are taken as measures for BDEs and are related to the stabilization of the radicals formed. This procedure has been recently applied to the subject of captodative stabilization (Bordwell and Lynch, 1989). Values of ABDE relative to the C—H BDE in methane are calculated according to (13). These values are set equal to the... 

In Figure 3, we have plotted the theoretical values of the ionization potentials for the polyenes and DPP versus 1/n on the same plot are experimental oxidation potentials (Eox) for DPP. An approximately linear correlation between IP and Eox is expected.(33) Furthermore, we have plotted the theoretical... 

Standard redox potentials are listed in Table 4.7. From Eq. (4.153), when only considering the half-reaction oxidation or reduction, an adequate reduction potential E red and oxidation potential Eox can be derived ... 

To be able to understand how computational approaches can and should be used for electrochemical prediction we first of all need to have a correct description of the precise aims. We start from the very basic lithium-ion cell operation that ideally involves two well-defined and reversible reduction and oxidation redox) reactions - one at each electrode/electrolyte interface - coordinated with the outer transport of electrons and internal transport of lithium ions between the positive and negative electrodes. However, in practice many other chemical and physical phenomena take place simultaneously, such as anion diffusion in the electrolyte and additional redox processes at the interfaces due to reduction and/or oxidation of electrolyte components (Fig. 9.1). Control of these additional phenomena is crucial to ensure safe and stable ceU operation and to optimize the overall cell performance. In general, computations can thus be used (1) to predict wanted redox reactions, for example the reduction potential E ) of a film-forming additive intended for a protective solid electrolyte interface (SEI) and (2) to predict unwanted redox reactions, for example the oxidation potential (Eox) limit of electrolyte solvents or anions. As outlined above, the additional redox reactions involve components of the electrolyte, which thus is a prime aim of the modelling. The working agenda of different electrolyte materials in the cell -and often the unwanted reactions - are addressed to be able to mitigate the limitations posed in a rational way. 

Theoretical calculations of oxidation potentials ox are based on a linear correlation of the first ionization potential Ip to the electrochemical oxidation potential Eox [274]. From a theoretical point of view, the linear correlation of the ionization potentials to oxidation potentials qx is based on Koopmans theorem [275], which states that the negative orbital energy Iihomo of the highest occupied molecular orbital (HOMO) equals the first ionization potential Ip. But this is only valid at H F... 

Figure 17.8 shows the electrochemical behavior of liPFe and the chelatoborates liDFOB and LiBOB atan Al-foil WE all three salts exhibitgood passivation of Al. At lower potentials, the current density i in the first cycle is very low and increases in the case of Li P Fj, first at 3.5 V and above vs Li/ Li due to electrolyte decomposition, much later with LiDFOB from 4.0 to 4.12 V (LiBOB) at an onset current density of 0.25 xA Cm . After reaching a maximum, a constant current appears that decreases further at the re-scan. This shows the formation of a protecting layer on the Al surface. This fact is also proved by the subsequent cycles, which show much later oxidative reactions. The resulting oxidation potential Eox of all three salts after passivation is about 4.9 V vs Li/Li+. LiBOB reaches this value after the third cycle. 

The success of this transformation depends upon the oxidation potential of the ESE group (Eox 1.5 V), which is lower than that of the alkyl silyl ether group (Eax 2.5 V). Recently, Schmittel et al.35 showed (by product studies) that the enol derivatives of sterically hindered ketones (e.g., 2,2-dimesityl-1-phenyletha-none) can indeed be readily oxidized to the corresponding cation radicals, radicals and a-carbonyl cations either chemically with standard one-electron oxidants (such as tris(/>-bromophenyl)aminium hexachloroantimonate or ceric ammonium nitrate) or electrochemically (equation 10). 

At the standard equilibrium potential eox = ered changing the electrode potential by an overpotential r/ lowers the energy of the oxidized state, where the electron has been transferred to the electrode, by —... 

TABLE 2. Oxidation potential and ionization potential of disilirane and digermirane Substrate Eox (V) vs SCE° 7p (eV)b... 

E°n, agrees closely with the oxidation potential of aggregated dye, the change in the Eox in... 

The oxidation potentials of TTF derivatives can be varied in a controlled way over a wide range by the introduction of appropriate substituents. The influence of substituents on oxidation potentials values of TTF has been discussed in many articles. For instance, the oxidation potentials of about 40 different substituted TTF derivatives have been measured under the same conditions [32]. In general, all substituents, with the exception of alkyl groups, increase oxidation potentials and the mesomeric effect of substituents have been shown to have an insignificant influence on the donor ability of TTF, in contrast to the trends observed for aromatic and heteroaromatic series. Some representative examples of oxidation potentials for substituted TTF derivatives are collected in Table 7. In the case of aryl-substituted TTFs, a usual Eox-cr+ correlation has been reported [63],... 

The fluorescence intensity of ZnP CONH Q is significantly quenched compared to the reference ZnP compound without Q due to efficient ET from the singlet excited state ( ZnP ) to Q in ZnP—CONH—Q (68). Such efficient ET results from the large driving force of electron transfer (—AGej = 0.91 eV in PhCN), which is determined from the one-electron oxidation potential of the ZnP moiety (Eox = 0-78V vs SCE), the one-electron reduction potential of the Q moiety (Ered = —0.36 V vs SCE), and the singlet excited-state energy of ZnP (2.05 eV). 

From the oxidation potentials provided above we have to conclude that oxidation will originate from the donor site (c) with the lowest Eox, which is indeed observed in the selective photoinduced electron-transfer (PET) cyanation of 1 using DAP + (A,A -dimethyl-2,7-diazapyreniumbistetrafluoroborate) as sensitizer [4]. 

Table 4. Structures, singlet or triplet energies (E or E ), reduction or oxidation potentials (Erdn or Eox), and excited state reduction or oxidation potentials (E rdn or E ox) of neutral organic acceptors and donors .

The oxidation potential of carbanions, Eox, or the reduction potential of carbocations, Ered, could be a practical scale of stability as defined by (3). These potentials can be measured by voltammetry, although the scale is subject to assumptions regarding elimination of the diffusional potential and solvation effects. 

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. 

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