Evaporated films of radioactive sodium chloride have been prepared by direct sublimation onto a water cooled quartz substrate at 10-⁵ mm of mercury. These possess specific surfaces of from 30-100 m²/g and show remarkably high exchange reactivity to chlorine. From kinetic studies using ³⁶Cl incorporated in the solid it has been found that the extent of exchange C follows a fractional power of the time C = at[superscript n] and that the rate is independent of surface area, so that the possibility of the rate controlling step involving diffusion is ruled out. These features had been reported in an earlier study but required confirmation with a wider range of specific surface and a modified procedure to measure surface area before reaction. The major part of the work is designed to elucidate the role of electronic defects in the exchange mechanism from the pressure and temperature dependence of the exchange rate and from the effect of introducing electronic defects by X-irradiation or fluoridation. These latter processes cause the kinetics of the reaction to change completely to a second-order law, and provide strong evidence to support an earlier tentative suggestion that electronic defects are involved in the reaction, and that a process of adsorption of a chlorine molecule into a pair of defects is important. Detailed mechanisms are proposed for both the power law and the second-order reactions, largely on the basis of the pressure dependence. Both mechanisms use two species of electronic defect, corresponding to Seitz's models for V₂ and V₄ centres, and the "power law" mechanism requires a transition complex between the two defects. Measurements by X-ray diffraction on the particle size in the evaporated films has shown them to be in the range 250-500 Å, and an estimate of the strain from the same results suggests that roughly one dislocation per particle is present. / Science, Faculty of / Chemistry, Department of / Graduate

The chemoselective hydrozirconation reaction of a series of 1-ene-3-yne molecules 51a-d, using the commercially available hydride reagent, Cp₂ZrCl(H) 1, provides an efficient route to the syntheses of 1,3-dienes 55a-d, substituted at the 1-position by the Cp₂ZrCl moiety. Similar chemoselectivity was observed in the hydrozirconation reaction of α, β-unsaturated nitriles, to generate the corresponding 1-azadienyl complexes 68-71. The complexes 55a-d were found to be useful general precursors in the preparation of other heterosubstituted 1,3-dienes. Thus, corresponding tin-, phosphorus-, boron-, selenium-and sulfur-heterosubstituted 1,3-dienes 77a-d, 79a-d, 87a-d, 88a-d and 89a-d were readily prepared in good to excellent yields by a stereoselective transfer reaction from zirconium. The 1-azadienyl complexes also served as useful starting materials in the preparation of selenium-and phosphorus-substituted 1-azadienes. The selenium-substituted 1,3-dienes 88a-d underwent a facile isomerization reaction when exposed to fluorescent light, and when thermolysed in the dark at 80°C in unsealed reactors. Mechanistic studies of this isomerization process suggested that an intermolecular pathway involving free radical intermediates was operable. A comparable photochemical isomerization reaction of the sulfur-substituted 1,3-dienes was also observed. When the cycloaddition reactions of 88a-b and 88d with maleic anhydride were performed in the absence of light at reson able temperatures, good yields of the expected endo-cycloadducts were obtained. However, when the same reactions were repeated in room light or at temperatures in excess of those required for formation of the endo-cycloadducts an, interesting, apparent [l,3]-shift of the phenylselenenyl moiety resulted. The results of a crossover experiment indicated that this rearrangment was intermolecular in nature. The preparation of the trialkylstannyl and phenylselenenyl 2-substituted 1,3-dienes (128 and 129) was achieved via a transmetalation reaction of the Grignard reagent 24. The Diels-Alder reactivity of 1,3-dienes 128 and 129, with a series of electron-deficient dienophiles, was successfully investigated. [Formula Omitted] / Science, Faculty of / Chemistry, Department of / Graduate

A connective Pummerer reaction was developed with a view to its use in the synthesis of analogues of ecteinascidin 597, a member of a family of potent anti-tumour natural products. A one-step synthesis of N-benzyl 2-hydroxyamides, involving the reaction of 2,2-dimethyl-1,3-dioxolan-4-one with amines, was investigated and the products were oxidised to give glyoxamides. Reaction conditions were optimised for the cyclisation of electron-rich N-benzyl glyoxamides in the presence of thiols and a Lewis acid (ZnCl2 or Sc(OTf)3) to give 4-sulfanyltetrahydroisoquinolinones, and mechanistic studies indicated the importance of hemithioacetal and thionium intermediates in these reactions. The scope of the reaction was found to encompass electron-rich N-benzyl pyruvamide substrates, which gave 4-methyl-4-sulfanyltetrahydroisoquinolinone products via what is believed to be a combination of thionium ion and cyclisation-substitution pathways. Under more forcing conditions, connective Pummerer cyclisation of N-benzyl 2,2-diethoxyacetamides was successful. Sharpless asymmetric aminohydroxylation and a Sharpless asymmetric dihydroxylation-Mitsunobu sequence were exploited in the synthesis of an enantioenriched 1,2-aminoalcohol. Subsequent conversion to branched, N-benzyl 2-hydroxyacetamides by PMB and silyl protection and N-acylation then oxidation and cyclisation furnished 1-silyloxymethyl-4-sulfanyl tetrahydroisoquinolinones. Modification of these tetrahydroisoquinolinones gave bridged macrolactones which map onto the A subunit of the ecteinascidins. A one-pot macrolactone synthesis using a connective Pummerer reaction was unsuccessfully attempted on a substrate bearing 2,2-diethoxyacetamide and thiol moiety in addition to an electron-rich benzene ring. A new protecting group strategy was necessary for continuation of the analogue synthesis and a variety of N,O-acetals were evaluated for the protection of the 1,2-aminoalcohol.

The preparation of bicyclic dienes of the general structures (72), (82), (83) and (162) is described. These materials have been prepared via a novel annulation sequence involving (a) the alkylation of various carbonyl containing substances with the donor acceptor reagents (43), (44), (108)-(114) and (154), (b) the conversion of the alkylation products into the enol triflates, and (c) the palladium(O) catalyzed intramolecular coupling of the enol triflate-vinylstannane moieties via either a "one" or "two pot" process. The Diels-Alder reactions of the "parent" bicyclic diene (75), the cisoid cis diene (145) and the cisoid trans diene (146) are described. Four basic questions regarding the face selectivity, regioselectivity, stereoselectivity and comparative reactivity of the dienes in the formation of the Diels-Alder adducts of general structure (174) are addressed. The annulation sequences described above have been applied to the first total syntheses of the dolastane diterpenoids (±)-(14S)-dolasta-1(15),7,9-trien-14-ol (239) and (±)-amijitrienol (242). Thus, the substituted cycloheptanone (262), prepared in seven steps from the commercially available material (261), was converted via a series of transformations, including the newly developed annulation process, into the bicyclic diene (264). Introduction of the two appendages to (264) proceeded stereoselectively to provide the keto vinylstannane (265). Ring closure was effected with the desired stereochemistry to yield (±)-(239). A reduction, deprotection sequence afforded the ketone (249) from the diene ketal (263). A series of three steps involving an aldol condensation, Swern oxidation and stereoselective methylation provided the diketone (290). Chemo- and stereoselective reduction of (290) followed by protection of the alcohol moiety yielded the silyl ether (303). Cyclization, according to the methodology described herein, and deprotection of the silyl ether moiety produced (±)-(242). [Formula Omitted] / Science, Faculty of / Chemistry, Department of / Graduate

This study examines the impact of reducing tick size and, in particular decimalization on stock splits. Based on previous studies, this study examines hypotheses in the following three areas: first, market reaction around stock split announcement and ex-dates, second, the effect of tick size on liquidity after stock split ex-dates, and third, the effect of tick size on return volatility after stock split ex-dates. The impact of tick size on market reaction around split announcement and ex-dates is measured by abnormal returns and buy and hold abnormal returns (BHARs). Also, this study investigates the long term impact of decimalization on market reaction for small, medium, and large firms for the three different tick size periods. The effect of tick size on liquidity after stock split ex-dates is measured by turnover, relative bid ask spread, and market maker count. The effect of tick size on return volatility around stock split announcement and ex-dates is measured by return standard deviation. Also, this study investigates the long term impact of decimalization on volatility after split ex-dates for small, medium, and large firms for three different tick size periods.

Artificial chemistries can be used to explore the generic properties of chemical reaction networks. In order to simulate for instance scenarios of prebiotic evolution the model must be close enough to real chemistry to allow at least semi-quantitative comparisons. One example is a previously described Toy Model that represents molecules as graphs, thereby neglecting 3D space, and employs a highly simplified version of the Extended H¨uckel Theory (EHT) to compute molecular properties. Here we show how the Toy Model can be extended to multiple phases by connecting the EHT calculations with chemical thermodynamics.

In this dissertation, we discuss spatiotemporal patterns in the wake of traveling waves in a microelectrode array (MEA) recording of a human epileptic seizure. In chapter two, we describe a method for estimating the direction of planar waves found in the last third of the seizure. We categorize the different phenomena that occur during those waves when projected along a one-dimensional slice in the domain. In chapter three, we summarize known examples of patterns in the wake of traveling wave solutions to reaction-diffusion systems. A brief review of results regarding the spectral stability of traveling wave solutions to reaction-diffusion equations is provided in chapter four. We review the essential spectrum and absolute spectrum, and summarize results about glued front-and-back pulse solutions. Using a reaction-diffusion model with Morris-Lecar dynamics, we present numerical experiments on a one-dimensional domain that exhibit spatiotemporal patterns in the wake of traveling waves. These patterns are precipitated by “backfiring” waves emitted from the primary wave in the opposite direction of initial travel, and qualitatively reproduce many of the features found in the last third of the seizure. A review of the model is given in chapter five. and a description of the phenomena found over an exhaustive set in a relevant parameter space of the model is given in chapter six. We compute branches of solutions in the parameter plane using numerical continuation in chapter seven. We describe the different types of solutions found along these branches. We present results on a curve of solutions where two branches of homoclinic orbits to equilibria in the moving coordinate frame meet at a heteroclinic loop, or T-point. We analyze the linear stability of solutions along this branch and draw comparisons to a known model that exhibits backfiring behavior. In chapter eight, we discuss seizure behavior in two spatial dimensions and present numerical experiments of the Morris-Lecar model in two dimensions. We describe results from backfiring waves initiated by a single point source and by two point sources in a two-dimensional domain. We show examples of simulations generated by two point sources that mimic the patterns in the empirical data.

This thesis presents the results of an experiment conducted to discover if selenic acid or monazite sand are possible catalysts that can be used for the alkylation of isobutane and isobutene.

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No description available.