Thesis (Ph.D.)--City University of Hong Kong, 2009. / "Submitted to Department of Biology and Chemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves 211-239)

The photochemical dissociation of hexafluoroacetone vapour (HFA) has been studied at room temperature using five exciting wavelengths between 2500 and 3500 Å, and at -78°, using 3130 Å excitation. The effect of the presence of biacetyl during the photolysis has been investigated. Complementary experiments on the visible emission from HFA were performed, paying particular attention to the quenching action of oxygen and biacetyl. Plots of reciprocal quantum yield of carbon monoxide versus HFA pressure have either a positive and constant, or positive and decreasing slope, down to 1 mm pressures there is virtually no evidence that a weak (multistage) collision mechanism is operative in deactivation of the excited molecules. A simple extension of classical unimolecular theory is examined, in order to account, for observed photo-dissociation rate constants, k₂(λ, T). The model shows that Arrhenius plots of k₂(T) at constant wavelength will not, in general, be linear, but that upper and lower limits for the critical (activation) energy, may still be obtained. For HFA, this energy is placed between 5.7 and 8.6 kcals/mole. Agreement in order-of-magnitude is found between calculated and observed values of k₂(T), only if it is assumed that a fraction (rather more than half) of the normal modes participate in intramolecular energy exchange. This fraction has to be increased with decreasing wavelength to explain the observed k₂(λ) values. The inadequacy of a classical treatment of the system is recognized. The emission spectrum of HFA consists of both fluorescence and phosphorescence. Small concentrations of biacetyl quench phosphorescence and triplet dissociation. The phosphorescence to fluorescence ratio is 2.77 at 25º and 9.95 at -78°, while the total emission yield increases by a factory of 16.7 on decreasing the temperature over this range. From a study of biacetyl emission, direct and sensitized by HFA, it is shown that nearly 50% of HFA molecules excited with 3130 Å, eventually reach the triplet state at 25º. The phosphorescence yield of HFA at -78°was estimated to be 0.51. At relatively high pressures, dissociation yields are apparently greater when less energetic excitation is used. Various modifications to the intersystem crossing mechanism are discussed to account for this, but no definite conclusion can be reached. / Science, Faculty of / Chemistry, Department of / Graduate

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 89-93). Also available on the World Wide Web.

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Thesis (Ph.D.) - University of St Andrews, May 2009. / Restricted until 29th May 2010.

This thesis deals with the abstraction of halogen atoms by trimethyl tin and trimethyl germanium radicals. Part I deals with the reactions of trimethyl tin radicals, produced by the photolysis of trimethyl tin hydride, in the presence of halogeno alkanes. Part II similarly deals with halogen abstraction using trimethyl germanium radicals produced by photolysis of trimethyl germanium hydride. A free radical chain mechanism appears to be operative in which a reaction scheme of the following form has been postulated. CH3)3M• + RX □(→┴(k2) ) (CH3)3MX + R• R• + (CH3)3MH □(→┴(k3) ) (CH3)3M•+ RH (CH3)3M• + (CH3)3M• □(→┴(k4) ) (CH3)3M-M(CH3)3 (M = Sn or Ge) Evidence supporting this mechanism includes the dependence of the formation of the alkane on the 1⁄2Type equation here. power of the light intensity, the non-existence of any other termination products and the thermodynamics of the overall initiation and propagation steps. The observed trends in abstraction rates, Br > C1 > F and for a particular halide tertiary > secondary > primary, are predicted by bond energy data and confirmed experimentally. Breaking of the C-X bond is hence of major importance in determining the relative rates of abstraction. Polar effects have been discussed in terms of the four factors put forward by Tedder and the properties of these two nucleophilic radicals have been discussed in terms of Coulombic repulsive and attractive forces due to electron displacement in the transition state. The change in reactivity, following substitution by electron withdrawing groups at the reaction site, provides evidence for the reversal of polar effects in the transition state. Substitution with electron withdrawing groups decreases the activation energy for halogen abstraction by trimethyl tin and trimethyl germanium radicals. However for hydrogen abstraction by chlorine atoms or trifluoromethyl radicals the activation energy is increased.

The thesis records the competitive addition reactions of CFBr2, CF2I, CHF2. and CH2F radicals to each of vinyl fluoride, 1,1-difluoroethylene, trifluoroethylene and tetrafluoroethylene in the presence of ethylene, and a few additional reactions in the absence of ethylene. The results are discussed in conjunction with the corresponding results for addition of C3F7, (CF3)2CF, C2F5, CF3, CF2Br, CC13 and CH3 radicals. Part 1 records the photolytic reactions of CFBr3. At short wavelengths both CFBr2 and CFBr are formed but the contribution to product formation from the carbene was insignificant in the kinetic series conducted at 366 nm. Competitive addition of CFBr2 gave, from the Arrhenius plots, the A-factor and activation energy differences and the relative rates of the addition steps. The activation energy differences showed a good correlation with atom localisation energies for C3F7, CF3, CF2Br, CC13 and CFBr2 radicals. The photolytic reactions of CHF2I and CH2FI with the fluoroethylenes are recorded in parts 2 and 3 respectively. The primary photolysis step with CHF2I gives difluoromethyl radicals and excited iodine atoms. The excited I (3P[sub]1⁄2) atoms abstract hydrogen from CHF2I giving a system containing both CHF2 and CF2I radicals. The Arrhenius plots for addition of CF2I radicals follow the same pattern as for CFBr2 with much reduced selectivity. Addition of difluoromethyl and fluoromethyl radicals, apart from the normal Arrhenius behaviour observed for competitive addition between ethylene and tetrafluoro-ethylene, show anomalous Arrhenius behaviour with negative slopes corresponding to diverging adduct ratios with increasing temperatures, and A-factors varying by up to three orders of magnitude. Several potential factors causing the anomalies are considered and excluded; dimerisation and cross combination of radical species; telomerisation of and hydrogen abstraction by the adduct radicals; elimination of HI from the adducts; and reversibility of the addition steps. The evidence favours joint participation of ground state (CHF2, CH2F) and vibrationally excited (CHF2, CH2F) radicals in non-reversible addition reactions, ground state radicals predominating at high temperature and excited state at low temperature. Analysis of the complete set of results indicates that, for fully halogenated alkyl radicals, orientation of addition to unsymmetrical fluoroethylenes is a function of steric factors: the logarithms of orientation ratios at 150°C give a linear correlation with radical radii. With partially halogenated alkyl radicals the strong polar differences between hydrogen and halogen atoms requires the introduction of a polar term, which, combined with radical radii, gives a linear correlation including both partially and fully halogenated alkyl radicals with logarithms of the orientation ratios.

The goal of this project was to synthesize a fluorinated disaccharide as a substrate or inhibitor for a glycosidase enzyme. A substrate analogue with only one strategically positioned fluorine atom could be used to probe such a complex interaction by using ¹⁹F NMR to monitor any changes in chemical shift, line width, and p coupling constants which arise when the analogue binds to the enzyme. Such changes would be more easily observed by using ¹⁹F NMR to monitor the perturbations around the single F nucleus than by monitoring the ¹H NMR because the spectrum in the latter case is much more complex due to the number of protons inherent in both the natural substrate and the enzyme. The compounds 3,4,6-tri-0-acetyl-2-deoxy-2-fluoro-α-D-glucopyranosyl bromide [5] and 2,3-di-0-acetyl-l,6-anhydro-β-D-glucose [2] were synthesized as appropriate starting materials and then coupled in diethyl ether in the presence of Ag₂CO₃, using AgSO₃CF₃ as a catalyst; these are the simple conditions of the well-known Koenigs-Knorr reaction. The coupling of a halosugar bearing a non-participating group at C-2 with an alcohol in low concentration has been shown by many other workers to result in a mixture of a- and 3-linked products, with the former being predominant. In this study, only the a-linked disaccharide 2,3-di-0-acetyl-l,6-anhydro-4-0-(3,4,6-tri-0-acetyl-2-deoxy-2-fluoro-α-D-glycopyranosyl)-B-D-glucopyranose [12] was obtained, the corresponding β-linked disaccharide was not observed in the reaction mixture. This fact suggests that some factor in either the reaction conditions employed or in the nature of the two sugars involved in the coupling was responsible for the exclusive production of only one type of linkage. The α-linked disaccharide [12] was deprotected to give the free sugar 2'-deoxy-2'-fluoro-maltose (4-0-(2-deoxy-2-fluoro-α-D-glucopyranosyl)-D-glucopyranose [14]) which is the C-2' fluorinated analogue of maltose. This compound should be a suitable probe for enzyme systems such as Maltase or α-glycosidase. The proton decoupled ¹⁹F NMR of [14] displayed two distinct resonances separated by 0.1 ppm which could be due to the α and β anomeric forms of that compound. The optical rotations values and the α/β anomeric ratios deduced from the ¹H NMR spectra for maltose and [14] were comparable, suggesting that this may indeed be the case. The synthesis of 4-0-(2-deoxy-2-fluoro-α-D-galacto-pyranosyl)-D-glucopyranose [17] was initiated with the view of using such a compound to study an α-galactosidase system; the partial synthesis of this molecule is also included herein. The conformational aspects of all the sugars synthesized in this work were deduced from ¹H NMR and then confirmed by ¹⁹F NMR and optical rotation. The ¹⁹F NMR spectra of the disaccharides were simple and were shown to provide sufficient information for the deduction of the conformational and configurational aspects of these sugars in the region of interest. This indicated that changes in the region about the fluorine could be monitored using ¹⁹F NMR and that these sugars could thus prove to be valuable probes for the elucidation of enzyme mechanisms. / Science, Faculty of / Chemistry, Department of / Graduate

Addition reactions of perf1uorothio1acetic acid (TFTAA) with organic and inorganic substrates were studied and six new compounds containing the trif1uoroacety1 group have been prepared. Two types of reactions were observed, free radical and nucleophilic addition. Under the influence of ultraviolet light, TFTAA (CF₃COSH) adds to olefins to form 1:1 adducts. The CF₃COS• radical appears to be the adding species. Three new olefin adducts were prepared: CF₃COSCFHCF₂H, CF₃COSCH₂CF₂H, and CF₃COSCH₂CFH₂. In addition, this was found to be a new way to prepare CF₃COSCH₂CH₃, which had been previously prepared by another route¹. Physical constants, analytical data, infrared, ultraviolet, nmr and mass spectra are presented supporting the proposed structures for these compounds. Nucleophilic addition adducts were formed with TFTAA and some organic and inorganic materials. TFTAA is a strong acid and the CF₃ COS⁻ ion was found to act as a nucleophile with several substrates. With hexafluoroacetone, addition of TFTAA across the carbonyl gave CF₃COSC(CF₃)₂OH. This structure is supported by analytical data, gas chromatographic data, infrared, ultraviolet, nmr, and mass spectra. Ethylene oxide and TFTAA react to produce the alcohol addition product, CF₃COSCH₂CH₂0H, which is supported by analytical data, nmr infrared, and mass spectra. Sulfur trioxide was studied as a representative inorganic molecule. TFTAA adds to this Lewis acid to form the sulfonate, (CF₃COS)₂S0₂. Analytical data, infrared, ultraviolet, nmr and mass spectra are reported here. All of the reactions, except the free radical reactions, occurred spontaneously and exothermically upon mixing the two reactants. A new method of preparing CF₃COSH, by reacting KSH with (CF₃CO)₂O, is also presented ¹M. Hauptschein, C.S. Stokes, and E.A. Nodiff, J. Am. Chem. Soc. 74, 4005 (1952)