Reactions of the cumyloxyl and benzyloxyl radicals with strong hydrogen bond acceptors. Large enhancements in hydrogen abstraction reactivity determined by substrate/radical hydrogen bonding

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DOIResolve DOI: http://doi.org/10.1021/jo3019889
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TypeArticle
Journal titleThe Journal of Organic Chemistry
ISSN0022-3263
1520-6904
Volume77
Issue23
Pages1047910487; # of pages: 9
AbstractA kinetic study on hydrogen abstraction from strong hydrogen bond acceptors such as DMSO, HMPA, and tributylphosphine oxide (TBPO) by the cumyloxyl (CumO•) and benzyloxyl (BnO•) radicals was carried out in acetonitrile. The reactions with CumO• were described in terms of a direct hydrogen abstraction mechanism, in line with the kinetic deuterium isotope effects, kH/kD, of 2.0 and 3.1 measured for reaction of this radical with DMSO/DMSO-d6 and HMPA/HMPA-d18. Very large increases in reactivity were observed on going from CumO• to BnO•, as evidenced by kH(BnO•)/kH(CumO•) ratios of 86, 4.8 × 10³, and 1.6 × 10^4 for the reactions with HMPA, TBPO, and DMSO, respectively. The kH/kD of 0.91 and 1.0 measured for the reactions of BnO• with DMSO/DMSO-d6 and HMPA/HMPA-d18, together with the kH(BnO•)/kH(CumO•) ratios, were explained on the basis of the formation of a hydrogen-bonded prereaction complex between the benzyloxyl α-C–H and the oxygen atom of the substrates followed by hydrogen abstraction. This is supported by theoretical calculations that show the formation of relatively strong prereaction complexes. These observations confirm that in alkoxyl radical reactions specific hydrogen bond interactions can dramatically influence the hydrogen abstraction reactivity, pointing toward the important role played by structural and electronic effects.
Publication date
LanguageEnglish
AffiliationSecurity and Disruptive Technologies; National Research Council Canada
Peer reviewedYes
NPARC number21268880
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Record identifierbc3ea7ad-7038-4227-ab35-a1b804d6d81c
Record created2013-11-21
Record modified2016-05-09
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