| Sujet | 2 ,4 ,6-trimethylphenol; Aromatic rings; Degree of Charge Transfer; Deuterium kinetic isotope effect; Hammett correlation; Hydrogen transfer; Hydrogen-atom transfer; Laser flash photolysis; Marcus cross-relations; N-oxyl radicals; Phenolic antioxidant; Phthalimide; Radical scavenging; Solvent effects; Stacking interaction; Theoretical calculations; Charge transfer; Deuterium; Free radical reactions; Hydrogen; Kinetics; Rate constants; Phenols; 2,2,5,7,8 pentamethylchroman 6 ol derivative; 2,6 di tert butyl 4 substituted phenol derivative; 2,6-dimethylphenol derivative; antioxidant; deuterium; hydrogen; phenol derivative; phthalimide derivative; phthalimide n oxyl radical; radical; scavenger; unclassified drug; chemical interaction; chemical structure; photolysis; transport kinetics |
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| Résumé | The kinetics of reactions of the phthalimide N-oxyl radical (PINO) with a series of activated phenols (2,2,5,7,8-pentamethylchroman-6-ol (PMC), 2,6-dimethyl- and 2,6-di-tert-butyl-4-substituted phenols) were investigated by laser flash photolysis in CH3CN and PhCl in order to establish if the reactions with PINO can provide a useful tool for evaluating the radical scavenging ability of phenolic antioxidants. On the basis of the small values of deuterium kinetic isotope effects, the relatively high and negative ρ values in the Hammett correlations and the results of theoretical calculations, we suggest that these reactions proceed by a hydrogen atom transfer (HAT) mechanism having a significant degree of charge transfer resulting from a π-stacked conformation between PINO and the aromatic ring of the phenols. Kinetic solvent effects were analyzed in detail for the hydrogen transfer from 2,4,6-trimethylphenol to PINO and the data obtained are in accordance with the Snelgrove-Ingold equation for HAT. Experimental rate constants for the reactions of PINO with activated phenols are in accordance with those predicted by applying the Marcus cross relation. © 2013 American Chemical Society. |
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