Para electron affinity

The one-electron reduction potentials, (E°) for the phenoxyl-phenolate and phenoxyl-phenol couples in water (pH 2-13.5) have been measured by kinetic [pulse radiolysis (41)] and electrochemical methods (cyclic voltammetry). Table I summarizes some important results (41-50). The effect of substituents in the para position relative to the OH group has been studied in some detail. Methyl, methoxy, and hydroxy substituents decrease the redox potentials making the phe-noxyls more easily accessible while acetyls and carboxyls increase these values (42). Merenyi and co-workers (49) found a linear Hammett plot of log K = E°l0.059 versus Op values of substituents (the inductive Hammett parameter) in the 4 position, where E° in volts is the one-electron reduction potential of 4-substituted phenoxyls. They also reported the bond dissociation energies, D(O-H) (and electron affinities), of these phenols that span the range 75.5 kcal mol 1 for 4-amino-... 

Similar results were obtained [139] with the three dimethoxybenzenes and acrylonitrile, methacrylonitrile, and crotonitrile. The amounts of substitution products decrease in the order acrylonitrile (49%) > methacrylonitrile (45%) > crotonitrile (6%), which agrees with the electron affinities of these compounds. Simultaneously, the amount of addition product increases acrylonitrile, 0% methacrylonitrile, 38% crotonitrile, 67%. In the series of anisole and the dimethoxybenzenes with crotonitrile, the amount of substitution products decrease in the order ortho- and para-dim ethoxy benzene > meta-dimethoxyben-zene > anisole, which is just the reverse of the order of their oxidation potentials. Ohashi et al. [139] have attempted to relate the photochemical behavior of these systems to the free enthalpy of electron transfer in the excited state as calculated with the Rehm-Weller equation, AG = E(D/D+) - E(A /A) - el/eR - AE00. 

The reactivity pattern suggests the presence of a strongly electrophilic oxidant. This is supported by the following observations [43]. For a series of para-substituted phenols, the rate of reaction decreased with increasing electronegativity of the para substituent, with an approximately linear correlation between the electron affinity of the substituent and the ratio of the log of the rate of oxidation of sub-... 

The electron affinities of the chlorinated biphenyls are lower than those of the chlorinated napthalenes. Nominal values are taken from Table 11.12. The temperature dependence of the three isomers of the monchlorobiphenyl will be similar to meta, ortho, and para dichlorobenzene data. Likewise, the temperature dependence of the compounds with two chlorines on the same ring will be similar to that of the trichlorobenzenes. The response of the fully chlorinated compound will be similar to that of hexachlorobenzene. The isomers with eight and nine chlorines only show nondissociative capture. Approximate curves for the chlorinated biphenyls are illustrated in Figure 11.13 and compared with experimental data obtained using the PDECD [45]. 

Another article concerning liquid-phase reactions catalyzed by perovskites is that by Sugunan and Meera (1995). They studied the reduction of ketones and oxidation of alcohol using RBO3 (R = La, Pr or Sr, B = Cr, Mn, Co or Ni) perovskites. Their goal was, however, to correlate data from these test reactions with surface electron-donor properties of these oxides. The electron-donor properties were investigated by the adsorption of electron acceptors with different electron affinities such as para- and /n-dinitrobenzene, benzoquinone, etc. They adsorbed these electron acceptors on both the mixed and the individual oxides. The results obtained are not conclusive to explain the catalytic behavior of the solids studied on the basis of this single property, as is often the case in many catalytic systems. 

Figure 1 Four one-electron donors D (1-4) with their first gas-phase ionization potentials four one-electron acceptors A (5-8) with their gas-phase electron affinities Aa, and three metals and one semimetal with their bulk work functions p. The abbreviations is N, N, N, Af -tetramethyl-para-phenylenediamine (TMPD), bisethylenedithiolene (BEDT), p-benzoquinone (BQ), and 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ).

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