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J Am Chem Soc. 2017 Nov 22;139(46):16650-16656. doi: 10.1021/jacs.7b07988. Epub 2017 Nov 9.

Bimodal Evans-Polanyi Relationships in Dioxirane Oxidations of sp3 C-H: Non-perfect Synchronization in Generation of Delocalized Radical Intermediates.

Liu F1,2, Yang Z2, Yu Y2,3, Mei Y1,4, Houk KN2.

Author information

1
State Key Laboratory of Precision Spectroscopy, School of Physics and Materials Science, East China Normal University , Shanghai 200062, China.
2
Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States.
3
Beijing Key Laboratory for Green Catalysis and Separation, Department of Chemistry and Chemical Engineering, Beijing University of Technology , Beijing 100124, China.
4
NYU-ECNU Center for Computational Chemistry at NYU Shanghai , Shanghai 200062, China.

Abstract

The selectivities in C-H oxidations of a variety of compounds by DMDO have been explored with density functional theory. There is a linear Evans-Polanyi-type correlation for saturated substrates. Activation energies correlate with reaction energies or, equivalently, BDEs (ΔHsat = 0.91*BDE - 67.8). Unsaturated compounds, such as alkenes, aromatics, and carbonyls, exhibit a different correlation for allylic and benzylic C-H bonds (ΔHunsat = 0.35*BDE - 13.1). Bernasconi's Principle of Non-Perfect Synchronization (NPS) is found to operate here. The origins of this phenomenon were analyzed by a Distortion/Interaction model. Computations indicate early transition states for H-abstractions from allylic and benzylic C-H bonds, but later transition states for the saturated. The reactivities are mainly modulated by the distortion energy and the degree of dissociation of the C-H bond. While the increase in barrier with higher BDE is not unexpected from the Evans-Polanyi relationship, two separate correlations, one for saturated compounds, and one for unsaturated leading to delocalized radicals, were unexpected.

PMID:
29069541
DOI:
10.1021/jacs.7b07988

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