No description available.

The PMR spectra of the two isomers of pyridine-2-aldehyde=2'-pyridyl hydrazone in carbon tetrachloride, dimethyl sulphoxide, and benzene solutions have been studied. Specific associations between PAPHY molecules and solvent molecules have been proposed to account for the observed solvent shifts. Dilution studies have shown that there are PAPHY-PAPHY molecular associations in solution. In the E-isomer these are of the n-donor type involving the lone pair electrons of the ring nitrogen atoms, whereas the Z-isomer association is a dipole-dipole interaction involving the aldehyde ring of different PAPHY molecules. Evidence from long range coupling shows that the uncomplexed E and Z-PAPHY molecules possess a different configuration to the complexed molecules. The chemical shift changes on isomerisation of the E to Z-isomer have been measured and those for the aldehyde ring are consistent with the withdrawal of charge from this ring via the nitrogen atom. Metal complexes of the two isomers of PAPHY have been prepared and their PMR spectra studied. The chemical shifts changes on complex formation have been interpreted in terms of the variation in magnetic anistropy of the ring nitrogen atoms in the ligand molecule and the degree of back donation of d-electrons from the metal atom.

No description available.

Ion chemistry has become increasingly important in the evolution of the chemical inventory of extraterrestrial environments. Isomers of ions have also come to play an important role as, in many instances, the cold environments in the interstellar medium and high layers of planet and satellite atmospheres do not supply enough energy to overcome isomerization barriers and the isomers effectively act as separate molecules.  In this licentiate thesis, several studies of the [CH3N]+ isomers are presented. Reactivity studies of the two isomers, the methanimine radical cation (H2CNH+) and aminomethylene (HCNH2+) with hydrocarbons C2H4, C2H2 and CH4, and IRPD spectroscopy of both species have been performed. Complimentary ab initio calculations aid in the determination of formation pathways of observed product channels and in the assignment of the vibrational bands seen in the IRPD spectrum. The results show that reaction pathways of the two isomers generally involve adduct formation followed by hydrogen ejection where the product or pathway is dependent on the ingoing reactant isomer. The IRPD spectrum allows identification of the different isomers via vibrational transitions. Isomer generation by electron ionization favours methanimine cation production with an abundance of 70% while with VUV photoionization it is possible to selectively produce isomers. It is concluded that isomerism must be considered when investigating the chemical environment of interstellar objects.

We have calculated the structures, the heats of hydrogenation and the resonance energies of benzene isomers. All structures and energies were calculated by using the MMX force fields. Using PC model, the calculated structure parameters of benzene's 8 isomers are generally in good agreements with the experimental data. The heats of hydrogenation and resonance energy of benzene isomers are parallel to those experimental data and need a. systematic adjustment of 4.5 kJ/mol.

Proceeding from the aim to reduce global pollution emissions from the continuous burning of hydrocarbons stimulated by increasing energy demand, more efficient and ultra-low emissions’ combustion concepts such as the homogenous charge compression ignition engines (HCCI) have been developed. These new engines rely on the low temperature chemistry (LTC) combustion concept. A detailed investigation of the properties of cool flames, governed by LTC, is essential for the design of these new engines. The primary goal of this work was to build a fundamental counterflow experiment for cool flames studies in a diffusive system, to better understand combustion in LTC engines. The project was intended to provide a basic understanding of the low-temperature reactivity and cool flames properties of butane isomers under atmospheric pressure conditions. This was achieved by establishing self-sustaining cool flames through a novel technique of ozone addition to an oxygen stream in a non-premixed counterflow model. The ignition and extinction limits of butane isomers’ cool flames have been investigated under a variety of strain rates. Results revealed that establishment of cool flames are favored at lower strain rates. Iso-butane was less reactive than n-butane by showing higher ignition and extinction limits. Ozone addition showed a significant influence on cool flame ignition and sustenance; it was found that increasing ozone concentration in the oxidizer stream dramatically increased the reactivity of both fuels. Results showed increased fuel reactivity as the temperature of the fuel stream outlet increased. 4 A numerical analysis was performed to simulate ignition and extinction of the cool flame in diffusive systems. The results revealed that ignition and extinction limits of cool flames are predominantly governed by LTC. The model qualitatively captured experimental trends for both fuels; however, it overpredicted both ignition and extinction limits under all strain rates and ozone concentrations. The discrepancies were within a factor of eight for the ignition limit and a factor of two for the extinction limit. Finally, sensitivity analyses were conducted to understand the reactions responsible for cool flames ignition. It was found that majority of the sensitive reactions are those that occur at low temperatures.

No description available.

No description available.

Porous cellulose nitrate membranes were impregnated with 8CB and PCH5 LCs (liquid crystals) and separations of solutes dissolved in aqueous phases were performed while monitoring solute concentration via UV-VIS spectrometry. The diffusing organic solutes, which consist of one aromatic ring and various functional groups, were selected to exclude molecular size effects on the diffusion and sorption. We studied the effects on solute transport of solute intra-molecular hydrogen bonding and solute/LC intermolecular hydrogen bonding. Hydrogen-bonding effects are a significant factor in the permeation selectivity of positional isomers. The reduction of available hydrogen-bond donors in aromatic ortho-isomers due to intramolecular H-bonding resulted in significant differences in the diffusion relative to the para-isomers which possessed more available H-bond donors. Solutes possessing multiple H-bonding interactions experienced a higher barrier to diffusion and, consequently, lower diffusivities. Diffusing solutes with a single available H-bond donor exhibited faster diffusion than solutes without H-bond donors. PCH5 embedded membranes showed higher solubility and diffusivity than the 8CB embedded membranes due to less dense molecular packing in PCH5 resulting from the bent cyclohexyl ring. The PCH5 LC membranes demonstrated enhanced permeation selectivity for hydroxybenzoic acid and aminophenol isomers primarily due to increased sorption selectivity. Shape selective absorption of rod-like para-isomers in the nematic phase was observed in both 8CB and PCH5 LCs. A nonchiral based HPLC-CD (High Performance Liquid Chromatography-CD) system was developed for the characterization of enantioselective separations. An enantioselective cholesteric liquid crystal membrane was fabricated and evaluated using the nonchiral HPLC-CD system. The cholesteric LC membrane showed enantioselectivity in the cholesteric phase where activation energies of permeation for 1-phenylethanol enantiomers were significantly increased due to the increased interactions between enantiomer and LC phase. The enantioselectivity increased with decreasing pore size of the membrane and increasing chiral dopant compositions. The selectivity decreases when there are no hydrogen bonding interactions between enantiomer and chiral dopant. / Ph. D.

<p> Investigations on the stability and reactions of various isomers of the benzohomotropylium/bridged [11]-annulene system are presented in this thesis. As 1,6-methano-[11]-annulenium cations are isomeric with benzohomotropylium cations in principle it is possible for these systems to be interconverted by a circumambulatory migration of the 'bridging' methano group. If this reaction were to proceed to equilibrium it would allow the examination of the thermodynamic stability of the various isomers.</p> <p> Homotropylium cations with two methyl groups at C8 are known to undergo facile circumambulatory rearrangements. Thus in this work the 1-hydroxy 8,8-dimethyl-2,3-benzohomotropylium and 1-hydroxy 8,8-dimethyl-4,5-benzohomotropylium cations have been prepared by protonation of the corresponding 2,3- and 4,5- benzohomotropones in FSO3H. On the basis of their 1H NMR spectra it is concluded that they can properly be regarded as homoaromatic cations. The thermal isomerizations of these cations have been studied in detail. The thermal isomerization of these cations led to the formation of a series of products but does not yield the corresponding [11]-annulenium isomer. In addition the barriers to ring inversion in these cations were found to be much lower than those of other homotropylium cations. This suggests that the former cations have a very open structure. Besides this experimental approach, the relative stability of these isomers has been explored using MNDO calculations. The calculated heats of formation (ΔHf) showed that the 1-benzohomotropylium cation is more stable than the corresponding [11]-annulenium ion by 21 kcal/mol.</p> / Thesis / Master of Science (MSc)