Origins of Selectivities and Reactivities in C−H Bond Activations: A Quantum Mechanical Investigation

Seminar series
Physical Chemistry Seminar
When
Thu, Apr 11 12:00pm
Where
2033 Young Hall
Speaker Lufeng Zou
University of California, Los Angeles
Dept. of Chemistry & Biochemistry
Description

 

C−H bond functionalization is a powerful method in organic synthesis, since it avoids prefunctionalization of substrates to introduce desired functionality. However, differentiating between numerous C−H bonds and effecting site specific and stereoselective chemical modifications is an ongoing challenge. In this talk, I will focus on the applications of quantum mechanical calculations to study C−H activations by organic and metallic reagents. Dimethyldioxirane (DMDO) is a non-metal C−H oxidation reagent. Site selectivities and reactivities in C−H activations by DMDO were studied in substituted cyclohexanes and trans-decalins, which are models of natural steroids. It is found that the release of 1,3−diaxial strain in the transition state contributes to the site selectivities and enhanced equatorial C−H bond reactivities for tertiary C−H bonds. C−H activation reactions that occur with the Grubbs metathesis catalyst were found to be controlled by closed−shell repulsions between the groups that chelate the ruthenium metal. Quantum mechanical computations with density functional theory (DFT) are widely used in modeling chemical reactions. By comparing the transition states associated with different mechanisms in a chemical reaction, insights into the determining factors in the activation energies could be provided, and the quantitative results were employed to investigate the stereoselectivities and reactivities in the reactions.

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