David Dolson (Committee Chair), Eric Fossum (Committee Member), Paul Seybold (Advisor)
Master of Science (MS)
Quantum chemical analysis was used to examine nucleophilic aromatic substitution reactions of fluorinated benzophenones, diphenyl sulfones, and triphenylphosphine oxides. Some experimental results for these compounds were contrary to conventional wisdom, which holds that calculated atomic charges for the aromatic sites and 13C-NMR and 19F-NMR chemical shifts should allow prediction of the preferred sites for aromatic substitution. Density functional theory (B3LYP/6-31+G*//RM1) and semi-empirical (RM1) quantum chemical calculations were employed to study the intermediates in the reaction pathways in order to identify the preferred paths for aromatic substitution. In most cases studied para substitution pathways had the lower energy intermediates and were favored.
Experimental acid dissociation pKa's for a set of 41 aliphatic carboxylic acids were compared with quantum chemical indices for the compounds in an attempt to find correlations that might help explain how the electronic structures of the compounds influence their tendencies to dissociate. The quantum chemical indices included the charges on atoms and groups of atoms, calculated vibrational frequencies, calculated nuclear magnetic resonance (NMR) chemical shifts, and reaction energy differences both in vacuum and in an aqueous phase solvent model. Several of these calculated quantities yielded respectable correlations, with the vibrational frequency of the carboxylic acid proton (R2 = 0.874) and the vibrational frequency of the carbonyl stretch of the carboxylate anion (R2 = 0.852) giving the best results. As was observed in earlier work, the RM1 semi-empirical calculations yielded better correlations than the more sophisticated density functional theory approach.
Department or Program
Department of Chemistry
Year Degree Awarded
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