Kinetic applications of electron paramagnetic resonance spectroscopy. 26. Quantum-mechanical tunneling in the isomerization of sterically hindered aryl radicals

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DOIResolve DOI: http://doi.org/10.1021/ja00438a005
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TypeArticle
Journal titleJournal of the American Chemical Society
ISSN0002-7863
Volume98
Issue22
Pages68036811; # of pages: 9
AbstractRate constants for the isomerization of 2,4,6-tri-tert-butylphenyl to 3,5-di-tert-butylneophyl have been measured from -26 to -160 °C, and for the corresponding isomerization of 2,4,6-tri-tert-(perdeuteriobutyl)phenyl from 20 to -150 °C. This pair of reactions has an exceptionally large deuterium kinetic isotope effect at all temperatures. Arrhenius plots for both reactions are nonlinear and over any range of temperature the activation energy and Arrhenius preexponential factor are much larger for deuterium than for hydrogen transfer. The experimental results can be quantitatively accounted for by quantummechanical tunneling through a potential barrier. The analogous isomerization of 2,4,6-tri(1′-adamantyl)phenyl, which was studied from -28 to -167 °C, also occurs by quantum-mechanical tunneling. Attempts to detect other aryl radicals by EPR spectroscopy are described.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21276562
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Record identifier79eaa2c0-229b-4b85-af48-26ad9cb0c3de
Record created2015-10-13
Record modified2016-05-09
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