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Abstract
Computational chemistry has been widely used to investigate chemical systems to infer properties about their structure and reactivity. Advent of modern density functional theory (DFT) methods has made computations on complex organic systems with 50-100 atoms amenable. Furthermore, the relative free energies and enthalpies of transition states for mechanistic investigations of organic reactions can be computed reliably using DFT methods. I have investigated various aza-thia cryptands with significant host-guest applications to elucidate their structure and their chelation tunability. I have also investigated the ground state structure of [18]annulene using multiple DFT and ab initio methods and explained the discrepancies between previous computational efforts and the X-ray crystallographic structure. I have also proposed a mechanistic pathway for the experimentally observed coalescence of NMR chemical shifts at elevated temperatures. I have proposed an electrostatic model to explain the observed stereo reversal in chiral metal phosphate catalysis compared to chiral phosphoric acid catalysis based on computational studies on an epoxide desymmetrization reaction. Finally, I have investigated the role played by hexafluoroisopropanol, a widely used polar solvent for C-H functionalization reactions, in a palladium catalyzed C-H alkylation reaction. Further, I have identified a silver-palladium bimetallic complex with two explicit hexafluoroisopropanol molecules as the lowest-lying pathway. I have used DFT methods and modern analysis techniques to investigate these complex organic systems and turn the numbers provided by computations into chemically meaningful insights and models.