A series of peroxyl radical clocks has been developed and calibrated based on the competition between the unimolecular beta-fragmentation (k(beta)) of a peroxyl radical and its bimolecular reaction with a hydrogen atom donor (k(H)). These clocks are based on either methyl linoleate or allylbenzene and were calibrated directly with alpha-tocopherol or methyl linoleate, which have well-established rate constants for reaction with peroxyl radicals (k(H-tocopherol) = 3.5 x 10(6) M(-1) s(-1), k(H-linoleate) = 62 M(-1) s(-1)). This peroxyl radical clock methodology has been successfully applied to determine inhibition and propagation rate constants ranging from 10(0) to 10(7) M(-1) s(-1).

A simple computational approach for predicting ground-state reduction potentials based upon gas phase geometry optimizations at a moderate level of density functional theory followed by single-point energy calculations at higher levels of theory in the gas phase or with polarizable continuum solvent models is described. Energies of the gas phase optimized geometries of the S0 and one-electron-reduced D0 states of 35 planar aromatic organic molecules spanning three distinct families of organic photooxidants are computed in the gas phase as well as well in implicit solvent with IPCM and CPCM solvent models. Correlation of the D0 - S0 energy difference (essentially an electron affinity) with experimental reduction potentials from the literature (in acetonitrile vs SCE) within a single family, or across families when solvent models are used, yield correlations with r(2) values in excess of 0.97 and residuals of about 100 mV or less, without resorting to computationally expensive vibrational calculations or thermodynamic cycles.

A method for predicting the ground state reduction potentials of organic molecules on the basis of the correlation of computed energy differences between the starting S(0) and one-electron-reduced D(0) species with experimental reduction potentials in acetonitrile has been expanded to cover 3.5 V of potential range and 74 compounds across 6 broad families of molecules. Utilizing the conductor-like polarizable continuum model of implicit solvent allows a global correlation that is computationally efficient and has improved accuracy, with r(2) > 0.98 in all cases and root mean square deviation errors of <90 mV (mean absolute deviations <70 mV) for either B3LYP/6-311+G(d,p) or B3LYP//6-31G(d) with an appropriate choice of radii (UAKS or UA0). The correlations are proven to be robust across a wide range of structures and potentials, including four larger (27-28 heavy atoms) and more conformationally flexible photochromic molecules not used in calibrating the correlation. The method is also proven to be robust to a number of minor student "mistakes" or methodological inconsistencies.

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