title: Competition H(D) kinetic isotope effects in the autoxidation of hydrocarbons.
abstract: Hydrogen atom transfer is central to many important radical chain sequences. We report here a method for determination of both the primary and secondary isotope effects for symmetrical substrates by the use of NMR. Intramolecular competition reactions were carried out on substrates having an increasing number of deuterium atoms at symmetry-related sites. Products that arise from peroxyl radical abstraction at each position of the various substrates reflect the competition rates for H(D) abstraction. The primary KIE for autoxidation of tetralin was determined to be 15.9 ± 1.4, a value that exceeds the maximum predicted by differences in H(D) zero-point energies (∼7) and strongly suggests that H atom abstraction by the peroxyl radical occurs with substantial quantum mechanical tunneling.
authors.affiliation: Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University , Nashville, Tennessee 37235, United States.
authors.forename: Hubert
authors.initials: H
authors.lastname: Muchalski
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Levonyak
authors.forename: Libin
authors.initials: L
authors.lastname: Xu
authors.forename: Keith U
authors.initials: KU
authors.lastname: Ingold
authors.forename: Ned A
authors.initials: NA
authors.lastname: Porter
mesh_terms: D003903:Deuterium / Q000737:chemistry*; D006838:Hydrocarbons / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010545:Peroxides / Q000737:chemistry
chemical_list: D006838:Hydrocarbons; D010545:Peroxides; C049375:perhydroxyl radical; D006859:Hydrogen; D003903:Deuterium