Computational Modeling of Oxyradical and Metal-Oxo Reactivity and Selectivity in Hydrogen Atom Transfer Reactions Restricted; Files Only

Abstract

Oxyradicals and metal-oxo species have proven to be useful tools in the selective oxidation of CH bonds. Understanding the reaction mechanisms, reactivities, and selectivities of these oxidations has been an important challenge in physical organic chemistry. A computational study was carried out to explore oxyradical and metal-oxo species to further trace the origins of their patterns in reactivity and selectivity as well as develop analogous models between metal-oxo catalysts and their oxyradical counterparts. Using density functional theory (DFT), the energetics of hydrogen abstraction reactions were probed with tert-butoxy, cumyloxy, and hydroxy radicals, as well as with a ruthenium-oxo bis(bipyridine) species, dubbed the Dubois-Sigman catalyst, and a non-heme iron-oxo PDP species, known as the White-Chen catalyst. It was found that a bimodal Evans-Polanyi relationship, divided by substrate type, was moderately useful in describing the kinetics of this set of oxyradicals and metal-oxo species. A modified EvansPolanyi relationship, known as the Roberts-Steel equation, was also applied to predict kinetic barriers of both oxyradicals and metal-oxo species. It was found that the Roberts-Steel functional form was unable to capture the variation in kinetics for metal-oxo species and was moderately successful for the range of alkoxy radicals explored in this work. It was suggested that a missing explanatory variable in the regression equation may resolve observed differences. Finally, a distortion-interaction analysis revealed that distortive effects that manifested in the transitionstate were mainly explained by developments along the reaction coordinate and correlated well with activation energy barriers. The White-Chen catalyst, uniquely, demonstrated elevated distortive effects in the transition-state more than those seen by other metal-oxo and oxyradical species, that requires further investigation. 

Table of Contents

1. Introduction

1.1. Iron-oxo Catalyzed HAT and Hydroxylation

1.2. Ruthenium-oxo Catalyzed HAT and Hydroxylation

2. Results and Discussion

3. Conclusions and Future Directions

4. Supplemental Information

4.1. Procedures for Density Functional Calculations

4.2. Thermodynamic and Kinetic Findings

4.3. Transition State Geometries

4.4. Cartesian Coordinates of Ground-State and Transition-state Optimizations

5. References

About this Honors Thesis

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School	Emory College
Department	Chemistry
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Chemistry, Physical Chemistry, Organic
Keyword	C-H functionalization Chemical reactions Reactivity Selectivity
Committee Chair / Thesis Advisor	Dr. Huw Davies, Emory University
Committee Members	Dr. Jamal Musaev, Emory University Dr. Frank McDonald, Emory University

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