The advancement of theoretical methods in recent years has allowed the calculation of highly accurate spectroscopic parameters. Comparing these values to the corresponding experimental data can allow molecular structures to be elucidated. This dissertation details the use of experimental and theoretical data from nuclear magnetic resonance (NMR) and fluorescence spectroscopy to determine structure. Herein the NMR focus is on measuring & modeling chemical shift anisotropy and one-bond carbon-carbon J-coupling constants (1JCC). The fluorescence analysis models vibrationally resolved fluorescence spectra. Chemical shift anisotropy techniques were used to study two conflicting crystal structures of the n-alkyl fatty acid, lauric acid. These two crystal structures differ only in their COOH conformation. Lattice-including density functional theory (DFT) refinements of each crystal structure failed to match experimental data leading to the proposal of a third crystal structure with a hydrogen disordered COOH moiety. This disorder strengthens the hydrogen bond providing a new rationalization to the long observed non-monotonic melting behavior of fatty acids having even and odd numbers of carbons. The INADEQUATE is a NMR experiment that directly establishes the skeleton of organic compounds by measuring the 1JCC throughout a molecule. The low occurrence of 13C-13C pairs (1 in 10,000) and breaks in connectivity due to the presence of heteroatoms causes challenges to INADEQUATE analysis. Here, the insensitivity problem is overcome using analysis software that automatically processes data and identifies signals, even when they are comparable in magnitude to noise. When combined with DFT 1JCC predictions,configuration and confirmations of the natural products 5-methylmellein and hydroheptelidic acid are elucidated. Vibrationally resolved fluorescence spectra of high molecular weight PAHs can be accurately calculated through time-dependent density functional theory (TD-DFT) methods. Here, the theoretical spectral profiles of certain PAHs are shown to match experimental high- resolution fluorescence spectra acquired at cryogenic temperatures. However, in all cases, theoretical spectra were systematically offset from experimental spectra. To decrease these uncertainties spectra were empirically corrected and an automated scheme employed to match theoretical spectra with all possible experimental spectra. In all cases the theoretical spectra were correctly matched to the experimental spectra.
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Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Powell, Jacob, "Measuring and Modeling NMR and Emission Spectra to Gain New Insight into Challenging Organic Compounds" (2017). Electronic Theses and Dissertations. 5708.