Kinetic applications of electron paramagnetic resonance spectroscopy. XVII. Secondary deuterium isotope effect and the absence of a "memory" in the β scission of a tetra-tert-butoxyphosphoranyl

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DOIResolve DOI: http://doi.org/10.1021/ja00840a035
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TypeArticle
Journal titleJournal of the American Chemical Society
ISSN0002-7863
Volume97
Issue7
Pages18131816; # of pages: 4
AbstractThe reaction of tri-tert-butyl phosphite with tert-butoxy radicals yields the phosphate and a tert-butyl radical via an intermediate tetra-tert-butoxyphosphoranyl radical. Using EPR spectroscopy and deuterium labeling, it has been shown that, at temperatures from 78 to -100°, this reaction occurs without any "memory" as to which tert-butoxy attacked the phosphite. However, the β scission of the phosphoranyl to phosphate and tert-butoxy exhibits a significant secondary β-deuterium isotope effect. After correction for the isotope effect involved in the disproportionation of tert-butyls (kd(CH3)3C/ kd(CD3)3C = 1.4 ± 02 from 80 to -20°, it being assumed that the combination rate constants kc(CH3)3C and kc(CD)3C are equal), the isotope effect per deuterium for decay of the phosphoranyl can be represented by log (kβH/kβD) = -0.029 + 0.063/θ where θ = 2.3RT kcal/mol. These isotope effects are discussed in relation to isotope effects in analogous reactions, and the advantages in terms of sensitivity and available temperature range of our procedure are pointed out.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21276522
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Record identifier5f98a613-042c-4715-8f5d-fefe668d1586
Record created2015-10-13
Record modified2016-05-09
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