Free energies of electron transfer

The isomerization is more effective when the (nitroanion-radical + alkali counterion) ion pair does not exist. The following needs to be noted It is assumed that intimate ion pairs possess larger electron affinity and are characterized by larger contribution to the free energy of electron transfer than free ions (Grigoriev et al. 2001). 

An increase in the cA-stilbene concentration favors the chain propagation and decreases the probability of termination when the DCNA anion-radicals react with the stilbene cation-radicals. A decrease in the irradiation intensity has a similar effect The chain propagation is the first-order process, whereas termination of the chains is the second-order process. A temperature rise accelerates the accumulation of the stilbene cation-radicals. In this system, the free energy of electron transfer is -53- —44 kJ moD (the cation-radical generation is in fact an endothermal process). If a polar solvent is substituted for a nonpolar one, the conversion of the cii-stilbene cation-radical into the trani-stilbene cation-radical deepens. Polar solvents break ion pairs, releasing free ion-radicals. The cA-stilbene cation-radicals isomerize more easily on being released. The stilbene cation-radical not shielded with a counterion has a more positive charge, and therefore, becomes stabilized in the... 

FIGURE 13. Arene fluorescence quenching constants versus the free energy of electron transfer to trans-stiIbene (O) and cis-stilbene (A). Dashed line is that obtained by Rehm and Weller (83a) for electron-transfer quenching. 

Calculations and Measurements of Free Energies of Electron Transfer 105... 

The Temperature Dependence of Rate Constants/Free Energies of Electron Transfer... 

Scheme 14 Mode selectivity as a function of free energy of electron transfer in photoreactions of benzene with olefins [lc, 78, 80].

Charge transfer has also been demonstrated in the reactions of excited cyano-substituted radicals (152,155) with a series of dienes [97]. Whereas reaction with the unsubstituted excited parent radicals is believed to involve H-atom transfer [95,97,101,106,116] (vide infra), correlation between the free energies of electron transfer and the observed quenching rates for excited 152 and 155 with 2,5-dimethyl-2,4-hexadiene and 1,3-cyclooctadiene indicates a charge transfer process. 

Sensitized PhotolysesAsF — lodobenzene + Quantum Yields ( ), Relative Polymerization Rates (RPR) and Free Energy of Electron Transfer ( AG)... 

Figure 6, Free energy of electron transfer. In order for electron transfer to occur from the excited sensitizer to the onium salt, AG must be negative (i.e., the electron transfer must be exothermic). AG can be calculated using half-wave redox potentials and excitation energies (see text).

Equation 5.2 Scaled equation for the free energy of electron transfer... 

The initial step in the addition reactions of arenes and aryl olefins with tertiary amines is electron transfer quenching of the singlet arene or aryl olefin acceptor by a ground state amine donor. The free energy of electron transfer can be calculated using Weller s equation (Eq. I) ... 

The Gibbs free energy of electron transfer is determined by the formal electron transfer potentials associated with the excited state of the metalloporphyrin ( p, ) and the redox couple in the organic phase... 

Figure 11.23. Photocurrent transient responses associated with the photo-oxidation of various ferrocene derivatives (a) and photoreduction of electron acceptors (b) by the ion pair ZnTPPS-ZnTMPyP. Experiments were performed at the water/DCE interface at 0 V (a) and —0.12 V(b). The difference in photocurrent magnitude is connected to the Gibbs free energy of electron transfer (see Table 11.1). Reprinted with permission fromrefs.[101] and [60]. Copyright (2002/2003) American Chemical Society.

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