Ph.D. / Organic Chemistry / The use of electron impact mass spectrometry for isotopic analysis is an established technique; however, its application to problems involving biologically produced molecules enriched in 13C has been severely limited. This limitation is shown to arise because of data reduction techniques which are, for practical purposes, incapable of dealing with the complex situation of multiple enrichment sites, limited isotope abundance, and complex spectral regions. Two approaches for detailed isotopic analysis of EIMS intensity are presented and illustrated using model data, literature data, and original data from biosynthetically enriched compounds. The first approach which allows for sequential variation of any one parameter is shown to be of value in experimental design through construction of ion cluster contour diagrams which summarize the variation of isotopic distribution, molecular size, and uncertainty in measurement with total isotopic content. The second approach differs in concept from previous methods and is especially promising for application to problems involving multiple sites of enrichment, limited isotopic abundance, and complex spectral regions. The key concept of this approach is that the roots of the polynomials constructed from observed spectral intensities are analytically related to the isotopic content and the isotopic distribution of the ions giving rise to the intensities.

This study consists of four major areas of research. First, the relationship between and was extended to Lrl nil homoallylic couplings and was used to determine the relative degree of puckering in a series of dihydroaromatic carboxylic acids. Second, the effect of coupling contributions transmitted through space were examined by theoretical calculations of the intermediate neglect of differential overlap finite perturbation theory type (INDO-FPT) including selective overlap reduction experiments to determine the sign and magnitude of the major through-space contributions and the effect of the orientation of the substituent upon the vicinal carbon3 carbon coupling. Third, the dependence of the J upon substituent orientation in norbornanes was empirically investigated by the synthesis of a series of lactones and cyclic ethers whose conformation was rigid and known. Fourth, a large number of norbornanes substituted with methyls in the 1, 3, and 7 position and a carbon-13 labeled substituent in the 2 position were synthesized and studied in order to obtain a variety of vicinal C-C couplings; all the NMR parameters for this series of compounds were determined while the carbon13 labeled substituent was varied from methyl to methylene to carbinol to aldehyde and to carboxylic acid.

Hu Hong Bing. / "May 2004." / "13" in title is superscript. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

No description available.

No description available.

A model system to calculate single-path coupling constant was devised to see if the couplings are additive in a system which has a dual-pathway. The system chosen was o-methyl-13C-benzoic acid. Because of anomalies in the data, the series was extended. Hybridization of the label appeared to have relatively little effect, and the conformation of the substituents very important.