UCLA

Molecular motion and chemical reactivity are two fundamental manifestations of molecular behavior, both of which are strongly influenced by their environments. In crystalline solids, carefully designed architectures can combine long-range structural order with substantial molecular freedom, giving rise to unusual dynamics and reactivity. In solution, interactions among substrates, catalysts, and solvents shape reaction pathways and selectivity. Computational chemistry provides a molecular-level framework for investigating these phenomena across distinct chemical environments. This dissertation presents a series of computational studies of molecular motion and chemical reactivity in crystalline and solution-phase systems.The first part of this dissertation, Chapters 1–4, examines the distinctive molecular dynamics and chemical reactivity that emerge in crystalline environments. Chapter 1 combines quantum mechanical calculations, molecular dynamics simulations, and NMR measurements to demonstrate gas-phase-like inertial rotation of cubane units in CUB-5, characterized by a nearly negligible rotational barrier and ultrafast gigahertz-scale dynamics. Chapter 2 extends this investigation to a series of cage-like rotors in isoreticular MOF-5 homologues, establishing a quantitative description of their rotational behavior, including inertia-dominated unidirectional motion, long-time Brownian diffusion, and differences in rotor–lattice coupling through a Langevin framework. Chapter 3 explores ground-state destabilization and dipole–dipole interactions in pillared paddle-wheel MOFs, showing how steric and electronic effects can tune rotational barriers and collective dipolar ordering. Chapter 4 turns from molecular motion to chemical reactivity in crystals, where calculations and experiments support a photochemically triggered thermal chain mechanism that amplifies the solid-state conversion of 2-azidobiphenyl derivatives relative to solution.The second part of the dissertation, Chapters 5–7, presents computational studies of catalytic organic reactions in solution. Chapter 5 investigates the N-heterocyclic carbene (NHC)-catalyzed radical acylfluoroalkylation of bicyclobutanes, where computational studies elucidate the formation of an NHC-derived ketyl radical and the origin of stereoselective radical–radical coupling. Chapter 6 describes a nickel-catalyzed, base-free Suzuki–Miyaura cross-coupling of organoboron reagents with aryl (pseudo)halides, where computational studies identify a cationic nickel(II) intermediate and reveal an electrophilic substitution pathway for the transmetalation step. Chapter 7 explores cobaloxime-catalyzed hydrogen atom transfer in the regiodivergent carbamoylation of branched alkenes, where computational studies reveal the steric origin of ligand-controlled regioselectivity.