Importance of π-stacking interactions in the hydrogen atom transfer reactions from activated phenols to short-lived N-oxyl radicals

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DOIResolve DOI: http://doi.org/10.1021/jo500789v
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TypeArticle
Journal titleJournal of Organic Chemistry
ISSN1520-6904
Volume79
Issue11
Pages52095218; # of pages: 10
SubjectAtoms; Bond strength (chemical); Hydrogen; Isomers; Phenols; Rate constants; Bond dissociation energies; Hydrogen atom transfers (HAT); Hydrogen-atom transfer; Laser flash photolysis; Phenolic antioxidant; Phenolic aromatic rings; Stacking interaction; Theoretical calculations; Free radical reactions; 6 hydroxy 2,2,5,7,8 pentamethylchroman; acetonitrile; antioxidant; caffeic acid; catechin; hydrogen; hydroxylamine; n oxyl radical; phenol derivative; phthalimide; quinazoline derivative; radical; triazine derivative; unclassified drug; article; chemical binding; density functional theory; dissociation; energy; enthalpy; gas; hydrogen bond; proton transport; solvent effect; time
AbstractA kinetic study of the hydrogen atom transfer from activated phenols (2,6-dimethyl- and 2,6-di-tert-butyl-4-substituted phenols, 2,2,5,7,8- pentamethylchroman-6-ol, caffeic acid, and (+)-cathechin) to a series of N-oxyl radical (4-substituted phthalimide-N-oxyl radicals (4-X-PINO), 6-substituted benzotriazole-N-oxyl radicals (6-Y-BTNO), 3-quinazolin-4-one-N-oxyl radical (QONO), and 3-benzotriazin-4-one-N-oxyl radical (BONO)), was carried out by laser flash photolysis in CH3CN. A significant effect of the N-oxyl radical structure on the hydrogen transfer rate constants (kH) was observed with kH values that monotonically increase with increasing NO-H bond dissociation energy (BDENO-H) of the N-hydroxylamines. The analysis of the kinetic data coupled to the results of theoretical calculations indicates that these reactions proceed by a hydrogen atom transfer (HAT) mechanism where the N-oxyl radical and the phenolic aromatic rings adopt a π-stacked arrangement. Theoretical calculations also showed pronounced structural effects of the N-oxyl radicals on the charge transfer occurring in the π-stacked conformation. Comparison of the kH values measured in this study with those previously reported for hydrogen atom transfer to the cumylperoxyl radical indicates that 6-CH3-BTNO is the best N-oxyl radical to be used as a model for evaluating the radical scavenging ability of phenolic antioxidants. © 2014 American Chemical Society.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC); National Institute for Nanotechnology (NINT-INNT)
Peer reviewedYes
NPARC number21272189
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Record identifierfd4989d0-0d76-4db8-8a09-943addb918f7
Record created2014-07-23
Record modified2016-05-09
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