Reactions of the Phthalimide N-Oxyl Radical (PINO) with Activated Phenols: The Contribution of 蟺-Stacking Interactions to Hydrogen Atom Transfer Rates

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• 作者：Claudio D鈥橝lfonso ; Massimo Bietti ; Gino A. DiLabio ; Osvaldo Lanzalunga ; Michela Salamone
• 刊名：The Journal of Organic Chemistry
• 出版年：2013
• 出版时间：February 1, 2013
• 年：2013
• 卷：78
• 期：3
• 页码：1026-1037
• 全文大小：708K
• 年卷期：v.78,no.3(February 1, 2013)
• ISSN：1520-6904

文摘

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 蟻 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 蟺-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.