Computational Investigation of Chemical Reactions: Exploring the Reactivity of Nickel Enoate and Fumarate Complexes, and Radical Assistance in the Force-Enabled Bond Scission of Poly(Acrylic Acid)

Abstract

Computational chemistry has emerged as a powerful tool in identifying the key chemical states that define the kinetics, thermodynamics, and the various selectivities of a chemical reaction. It allows for a greater understanding of chemical processes by providing insights that would be difficult to achieve through direct experimentation alone. Herein are described three examples where computational analysis is used to provide insight into chemical reactions. In Chapter 1, some fundamentals of computational research in chemistry is described. Topics include the potential energy surface, the computational methods used for energy calculation, and transition state finding using the growing string method. The tools described in this chapter are used in the subsequent chapters. Chapter 2 investigates the mechanism of a nickel-catalyzed [3+2] alkylative cycloaddition. Prior experimental work has suggested multiple possible mechanisms, which are interrogated here computationally. Two distinct mechanisms are found to be in a precarious balance with each other, and small perturbations in the substrates used in the reaction are found to tilt the balance towards one mechanism over the other. The findings from this chapter have implications for the mechanism of [3+2] alkylative cycloadditions as a whole, including the activation process detailed in Chapter 3. In Chapter 3, the activation process of air-stable nickel fumarate catalysts is studied. The original hypothesis of fumarate dissociation as a mechanism of activation was overturned after computational analysis determined a fumarate consumption event must occur instead. These findings inspired subsequent experimental work that isolated the products of fumarate dissociation, and found that catalyst activation goes through a similar [3+2] alkylative cycloaddition detailed in Chapter 2. Through this lens, the mechanisms of activation of active IMes catalyst and inactive BAC catalyst are evaluated computationally, to provided a rationale for why one catalyst works and the other does not. Using these insights, preliminary investigations towards improving the BAC catalyst are performed. Chapter 4 details the effect of radical attack on the tensile strength of poly(acrylic acid) (PAA). Two different methods are used to determine how radical attack weakens the tensile strength of the polymer backbone. Additionally, the effect of force in the radical-free and radical-abstracted cases on the geometry of the starting structures and transistion state of the species involved in bond scission is observed. The different behaviors between the two regimes are attributed to the differences in the curvature of their potential energy surfaces. The findings of this chapter carry implications for the development of new depolymerization reactions. Finally, Chapter 5 summarizes the work, and provides final thoughts on future directions. Elements of this work are compared to the Gettier problem, and the symbiotic relationship between theorists and experimentalists is discussed.