Hydrogen atom abstraction reactions from tertiary amines by benzyloxyl and cumyloxyl radicals: Influence of structure on the rate-determining formation of a hydrogen-bonded prereaction complex

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DOIResolve DOI: http://doi.org/10.1021/jo201025j
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TypeArticle
Journal titleJournal of Organic Chemistry
ISSN0022-3263
Volume76
Issue15
Pages62646270; # of pages: 7
SubjectAmine structures; Cyclic amines; Diffusion limits; Hydrogen atom abstraction; Lone pair; Overall reactions; Prereaction complexes; Tertiary amine; Time-resolved kinetic study; Abstracting; Amines; Atoms; Complexation; Deuterium; Rate constants; Hydrogen; benzyloxyl; chemical compound; cumyloxyl; hydrogen; nitrogen; pempidine; tertiary amine; unclassified drug; article; chemical reaction; chemical structure; kinetics; Amines; Benzyl Compounds; Free Radicals; Hydrogen; Hydrogen Bonding; Models, Chemical; Molecular Structure
AbstractA time-resolved kinetic study on the hydrogen atom abstraction reactions from a series of tertiary amines by the cumyloxyl (CumO •) and benzyloxyl (BnO •) radicals was carried out. With the sterically hindered triisobutylamine, comparable hydrogen atom abstraction rate constants (k H) were measured for the two radicals (k H(BnO •)/k H(CumO •) = 2.8), and the reactions were described as direct hydrogen atom abstractions. With the other amines, increases in k H(BnO •)/k H(CumO •) ratios of 13 to 2027 times were observed. k H approaches the diffusion limit in the reactions between BnO • and unhindered cyclic and bicyiclic amines, whereas a decrease in reactivity is observed with acyclic amines and with the hindered cyclic amine 1,2,2,6,6-pentamethylpiperidine. These results provide additional support to our hypothesis that the reaction proceeds through the rate-determining formation of a C-H/N hydrogen-bonded prereaction complex between the benzyloxyl α-C-H and the nitrogen lone pair wherein hydrogen atom abstraction occurs, and demonstrate the important role of amine structure on the overall reaction mechanism. Additional mechanistic information in support of this picture is obtained from the study of the reactions of the amines with a deuterated benzyloxyl radical (PhCD 2O •, BnO •- d 2) and the 3,5-di-tert-butylbenzyloxyl radical. © 2011 American Chemical Society.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC); National Institute for Nanotechnology (NINT-INNT)
Peer reviewedYes
NPARC number21271359
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Record identifier8974ecdd-9a43-4576-8102-1471f56821a8
Record created2014-03-24
Record modified2016-05-09
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