Calibration of a new horologery of fast radical "clocks". Ring-opening rates for ring- and α-alkyl-substituted cyclopropylcarbinyl radicals and for the bicyclo[2.1.0]pent-2-yl radical

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DOIResolve DOI: http://doi.org/10.1021/ja00015a024
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TypeArticle
Journal titleJournal of the American Chemical Society
ISSN0002-7863
Volume113
Issue15
Pages56875698; # of pages: 12
AbstractRate constants have been determined at 37°C for the ring opening of a variety of alkyl-substituted cyclopropylcarbinyl radical "clocks" by nitroxide radical trapping (NRT) using TEMPO. Relative yields of unrearranged and rearranged trialkylhydroxylamines were measured at various TEMPO concentrations, and these data were then combined with absolute rate constants for the reactions of structurally appropriate alkyl radicals with TEMPO as determined by laser flash photolysis. Cyclopropylcarbinyl radicals, including the bicyclo[2.1.0]pent-2-yl radical, were generated by H-atom abstraction from the parent hydrocarbon and, in a few cases, also from the appropriate diacyl peroxide. Twelve substrates yielded sixteen clock reactions because some cyclopropylcarbinyls can undergo two different ring-opening reactions. For six methyl-substituted cyclopropylcarbinyls rate constants ranged from 0.8 × 108 s-1 for 1-methylcyclopropylcarbinyl to 47 × 108 s-1 for pentamethylcyclopropylcarbinyl. Rate constants for the ring opening of cyclopropylcarbinyl, α-methyl- and α,α-dimethylcyclopropylcarbinyl are 1.2, 0.70, and 0.88 × 108 s-1, respectively. Rate constants for H-atom abstraction by tert-butoxyl from various positions in the 12 cyclopropane substrates relative to the rate of H-atom abstraction from cyclopentane have also been determined by using competitive NRT.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21276505
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Record identifier4d416310-e141-4470-9344-51e45f8d464d
Record created2015-10-13
Record modified2016-05-09
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