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A series of studies are presented in which fluorine tagging reagents are used to analyze complex mixtures for compounds containing active hydrogen functional groups (e.g., hydroxyl, amine, thiol, and carboxylic groups). The existence of these derivatized functional groups is determined by utilizing a number of solution and solid-state nuclear magnetic resonance (NMR) techniques. In solution NMR studies p-fluorobenzoyl chloride was the fluorine tagging reagent of choice because of a large ¹⁹F chemical shift range for the different derivatized substrates (~10 ppm) and generally good reaction yields. Various classes of sterol and amino acid p-fluorobenzoyl derivatives were characterized on the basis of their ¹⁹F NMR isotropic chemical shifts. The presence (or absence) of hydroxyl, amine, and carboxylic acid functional groups in coal extract and pyrolysis products was also determined. The versatility of the p-fluorobenzoyl chloride as the fluorine tagging reagent in ¹⁹F NMR was enhanced by: a) enriching the carbonyl carbon of the acid chloride with labeled ¹³C isotope, thus synthesizing a dual ¹⁹F and ¹³C NMR sensitive reagent and b) using the reagent in conjunction with LC-NMR. The extension to either technique added another dimension to the NMR spectral data obtained from the p-fluorobenzoyl tagging reagent in solution NMR. Finally, preliminary data is presented illustrating how fluorine tagging reagents may be used to study functional groups (and atoms present in the immediate proximity of the group) existing on solid material utilizing solid-state NMR. Functional groups on the solid material are tagged with a fluorinated reagent. The sample is then analyzed using solid-state NMR with cross-polarization (CP), magic angle spinning (MAS), and high-power proton decoupling. The ¹⁹F dipolar coupling interactions, created by the presence of the fluorine tag, attenuate signals for these nuclei in the immediate proximity of the tagged site. A series of 1-adamantanol, steroid, and silica gel fluorinated derivatives show that the effects of the ¹⁹F dipolar interactions were modulated by complex anisotropic molecular motions (i.e., solid system with little motion, exhibiting greater signal attenuations due to ¹⁹F dipolar coupling). / Ph. D. / incomplete_metadata

The limitations of previous dynamic nuclear polarization (DNP) experiments have been avoided by a transfer DNP approach whereby the nuclear spins are polarized by DNP at low magnetic field (0.33 T) and then quickly transferred to a high monitoring field (4.7 T). This approach provides an order of magnitude improvement in sensitivity when compared to the usual low field DNP experiment. Also high resolution spectra commonly obtainable at high magnetic fields are now possible for the DNP enhanced signals. Using this method, we have observed large ¹H, ²D, ¹³C, ²⁹Si, and ¹⁵N scalar and dipolar enhancements (2-60 times of signal strength at 4.7 T NMR). Among the results, ¹⁵N and ²⁹Si liquid DNP enhancements are the first to be reported. The selective ¹³C and ¹H DNP enhancements at 0.33 T for different nuclei on the same molecule were observed. A mathematical model describing the low to high magnetic field transfer DNP experiments has also been developed. In ¹³C DNP, we find that the three-spin effect can significantly degrade the dipolar dominated enhancements unless high radical concentrations are used. The scalar dominated ¹³C DNP enhancements can be very large. In addition, the nitroxide radical (TEMPO) used in the present study can induce large scalar enhancements at carbon or nitrogen atoms which have weakly acidic hydrogens. These results indicate DNP can be a very sensitive probe to study weak intermolecular interactions (e.g., hydrogen bonding). / Ph. D.

In this study the applicability of Carbon-13 NMR and XPS to the detection of chemical changes in a solid composite rocket propellant was studied. Storage at elevated temperatures was used to simulate the propellant ageing process. In the XPS analysis, changes in the sources for the N(1s) and Cl(2p) photopeaks were investigated. The propellant loses "organic" nitrogen as it ages. Changes in the amount of Cl⁻ present are in doubt due to instrumental considerations. Carbon-13 NMR analysis showed that with increasing age of a sample there is a corresponding loss of vinylic groups from the binder. This loss of vinylic character is preferential in the order pendant>>cis>trans. Due to the long scan times involved this method is of limited utility for ageing analysis. / Master of Science

In this thesis, I traced the development of Nuclear Magnetic Resonance (NMR) Spectroscopy through the pages of the Journal of Organic Chemistry (JOC) from the year 1956 to 1969 to understand how organic chemists and Varian Associates?the makers of the first commercial NMR spectrometers?negotiated the identity of the NMR spectrometer. The work of the organic chemists was examined through their publications in the JOC. Examining the abstracts from the JOC between the years 1956 and 1969 developed an understanding of the ways in which organic chemists used the instrument. To understand the role Varian Associates played in the development of NMR, I examined the company?s advertisements in the JOC. I traced the changes in advertising style and format in order to see how Varian Associates expected their instruments to be used. I drew three conclusions from this work: 1) organic chemists and Varian Associates together determined what an NMR spectrometer was and how it could be used; 2) the identity of the instrument was negotiated by these two groups, and the novel use of the instrument by the organic chemists and new schemes in advertising on the part of Varian Associates were attempts to shift this identity; 3) NMR spectroscopy was a domain of knowledge that was embodied in the NMR spectrometer, and that could only be accessed through the instrument. / Master of Science

Nuclear Magnetic Resonance (NMR) and computational methods increasingly play a predominant and indispensable role in modern chemical research. The insights into the local nuclear environment that NMR can provide is unique information which allows the structural characterization of novel materials, as well as the understanding and explanation of their relevant properties on an atomic scale. Computational methods, on the other hand, can be used to support experimental findings, providing a rigorous theoretical basis. Furthermore, when more complex chemical systems are considered, calculations can prove to be invaluable for the interpretation of experimental data and often allow an otherwise impossible spectral assignment. This thesis presents a series of studies in which NMR spectroscopy, in combination with computational methods, is utilized to investigate a variety of chemical systems both in solution and the solid state. An overview of the thesis and experimental and computational details are given in Chapter 1. In Chapter 2, the quantum mechanical basis necessary for the description of the NMR phenomenon is presented. Chapter 3 explores the main experimental techniques employed routinely for the acquisition of NMR spectra in both solution and the solid state. Chapter 4 describes the main features of density functional theory (DFT) and its implementation in computational methods for the calculation of relevant NMR parameters. Chapter 5 reports an experimental solution-phase NMR study and a parallel computational investigation of the poly(CTFE-co-EVE) fluoropolymer. In Chapter 6, the combination of [superscript(14/15)]N solution-phase NMR techniques and DFT methods for the study of alkylammonium cationic templates used in the synthesis of microporous materials is presented. The characterization of a boroxoaromatic compound in the solid state and the study of its reactivity are described in Chapter 7. In Chapter 8, two experimental NMR methods for the study of the anisotropic chemical shift interaction in the solid state are compared and used to characterize a range of materials. Cross-polarization and nutation of quadrupolar nuclei are computationally investigated under both static and spinning conditions in Chapter 9. A general conclusion and a summary are given in Chapter 10.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Please refer to full text for abstract. Abstract contains special characters.