Chromatographic methods were used to determine the absolute values of cis-aconitic acid and trans-aconitic acid present in sugar cane factory processing streams and to determine the rates of isomerisation from the trans-aconitic acid to the cis-aconitic acid isomer. A reproducible, solid phase, ion exchange extraction method was developed to isolate the organic acids found in sugar factory process streams. The isolated acids were quantified using a dual ion-exclusion column, high performance liquid chromatographic method. To improve resolution of the acids, columns were maintained at different temperatures, whilst the combined use of both ultra-violet (UV) and refractive index detection proved useful in peak identification. Concentrations of the aconitic acid isomers were used to calculate the cis/trans aconitic acid isomer ratio occurring across the different processes found in a sugar cane factory. trans-Aconitic acid was found to be the predominant form present in the cane entering the factory. Analysis showed that isomerisation of the trans-aconitic acid to the cis-aconitic acid isomer occurred during processing. To understand and model this reaction, a reproducible experimental isomerisation method was developed making use of buffers to maintain pH conditions during experiments. A chromatographic analysis method, using ion-exclusion chromatography and UV detection, was developed to analyse the isomerisation reaction mixture. Chromatography was used in both an on-line and off-line mode for quantitation of the isomers. The method was used to study the isomerisation under conditions similar to those found in the factory. These included pH, temperature, ionic strength and the presence of monovalent and divalent cations found in sugar cane juices. It was shown that the isomerisation is a first order reversible reaction under the conditions studied. Temperature and pH were shown to be the important isomerisation variables. Temperature enhances the rate of isomerisation of the trans-aconitic isomer to the cis-aconitic acid isomer whilst pH affects the ultimate cis/trans aconitic acid ratio attained. Ionic strength was found to be a relatively unimportant factor. The presence of divalent and monovalent cations, at concentrations usually found in cane juice, was shown to have little effect on the rate of isomerisation. Activation parameters, including the activation energy (Ea), pre-exponential factor (log A), enthalpy (?H‡) and entropy of activation (?S‡), were calculated at each combination of buffer concentration and pH used in the experimental procedures. The values recorded are of a similar value to those reported for structurally similar compounds. cis-Aconitic acid was shown to undergo decarboxylation to itaconic acid. This occurred at low pH values and high temperatures. A detailed study was not undertaken since the conditions under which it occurs are considered extreme from the viewpoint of a sugar technologist. A model describing the equilibrium cis/trans aconitic acid isomer ratio was developed as a function of pH, temperature and time from the kinetic results. This was used to predict the equilibrium ratio for the aconitic acid isomers at the output of various processes in the sugar factory. Given the time, average pH and temperature the model can successfully predict the equilibrium ratio for the relevant process stream. / Thesis (M.Sc.)-University of Natal, Durban, 2000.

Thesis advisor: Marc L. Snapper / Tandem Reactions have proven themselves to be useful reactions for the synthesis of highly complex materials. Ruthenium alkylidenes are shown to be useful precursors for the development of new tandem processes. First, a new tandem metathesis/hetero-Pauson-Khand process is developed using Grubbs' second generation catalyst. Next, various metatheis/olefin isomerization processes are explored. / Thesis (PhD) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This thesis describes applications in co-crystal reactivity, structure determination, and mechanochemical preparation. We also investigate the solution-phase reactivities of products derived from a template-directed synthesis. Specifically, we described the acid treatment of an achiral molecular ladder of C2h symmetry composed of five edge-sharing cyclobutane rings, or a [5]-ladderane, with acid results in cis- to trans- isomerization and/or oxidation of end pyridyl groups. Solution NMR spectroscopy and quantum chemical calculations support the isomerization to generate two diastereomers; namely, an achiral and a unique chiral ladderane. The NMR data, however, could not lead to unambiguous configurational assignments of the two isomers. Single-crystal X-ray diffraction was employed to determine each configuration. One isomer readily crystallized as a pure form and X-ray diffraction revealed the molecule as being achiral based on Ci symmetry. The second isomer resisted crystallization under a variety of conditions. Consequently, a strategy based on a co-crystallization was developed to generate single crystals of the second isomer. Co-crystallization of the isomer with a carboxylic acid readily afforded single crystals that confirmed a chiral ladderane based on C2 symmetry. We also demonstrate how the stereochemistry can be retained upon treatment with acid. It will be shown how a monocyclobutane can be used as a model system when investigating the reactivity of the [5]-ladderane. While investigating the reactivity of a diene diacid we determined that a bicyclobutyl that bears six carboxylic acid groups results from a trimerization of the solid in pure form in the solid state. Powder X-ray diffraction and a co-crystallization are used to solve the structure of the diene and elucidate the stereochemistry of the bicyclobutyl, respectively. Having established the reactivity of the diene diacid we used hydrogen-bond-acceptor (HBA) templates to assemble the diacid in the solid state in a photoactive solid for an intermolecular [2 + 2] photocycloaddition as well as a photostable solid. To enhance strategies to generate stereocontrolled products derived from reactive co-crystals mechanochemical methods were applied to eliminate or reduce the solvent used to prepare the co-crystal solids. In particular, we show how supermolecules with olefins organized by hydrogen-bond donor and acceptor templates that react in the solid state rapidly form co-crystals via solvent-free and liquid-assisted grinding.

Nitromethane is the simplest organic-nitro compound as well as the archetype of an important class of high explosive. Homogeneous nitromethane reactions have been the subject of extensive studies. Particularly the unimolecular isomerization of nitromethane to methyl nitrite is proven to be competitive with simple C-N bond (bond energy 60 kcal/mol) rupture. The activation energy for the rearrangement was measured to be 55.5 kcal/mol and methyl nitrite has a very weak CH3O-NO bond energy 42 kcal/mol lower than that for homolysis. The thermal chemistry of nitromethane on Cu(111) was studied by a combination of temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) techniques. TPD spectra show that the desorption features include the physisorbed multilayer and monolayer of CH3NO2 at 150 and 190 K, respectively. The major decomposition pathway is via cleavage of O-N bond to yield a major product NO, which is characterized by m/z 30(NO+). A possible contribution from isomerization of nitromethane to methyl nitrite (CH3NO2 CH3ONO) on the surface cannot be ruled out at 278 K. In addition to isomerization, the dehydrogenation products CO and CO2 are also unveiled as part of the desorption features at 314 and 455 K, respectively. We can further prove the reactivity of nitromethane on Cu(111) at 367 K by using the deuterated form of nitromethane which reveals the corresponding desorption TPR/D signals of D2, D2O and CD4. However, we find that nitromethane also reacts by dissociating the C-H bond and the O-N bond, however, leaving the C-N bond intact. Along this reaction channel, HCN desorbs as a product above 360 K, as evidenced by a broad desorption feature of m/z 27. Dimerization of CN to C2N2 occurs at 815 K. The RAIR spectroscopy demonstrates that nitromethane is indeed adsorbed on Cu(111) at 100 K. The formation of methoxy and formyl are supported by the observation of desorption of NO at 278 K with the characteristic NO stretching mode found at 1535 cm-1. Moreover, we assign side-bonded CN and aminomethylene (HC-NH2) present on Cu(111). After the surface is annealed to 330 K, a signature band at 2173 cm-1 is assigned to terminal-bounded CN stretching mode. This band eventually fades out above 900 K consistent with the evolution of cyanogen at 815 K.

Thesis (M. Sc.)--University of Canterbury, 2009. / Typescript (photocopy). "June 2009." Includes bibliographical references. Also available via the World Wide Web.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 136-143). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 136-143). Also available on the Internet.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, August 2001. / Includes bibliographical references. Also available on the Internet.

The gas-phase chemistry of butanal, propanal, and acetaldehyde has been investigated using electron bombardment matrix isolation techniques. Each aldehyde was diluted in excess argon gas and subjected to electron bombardment with 300eV electrons. The products of subsequent reaction processes were matrix isolated and analyzed by FTIR absorption spectroscopy. Ionized butanal produced a variety of decomposition products including propane, propene, propyne, ethene, ethyne, CCCO, ketene, formaldehyde, CO, CH2=CHCH2•, CH2CHO•, HCO• and methane. Products resulting from ionized propanal included the ethyl radical, ethane, ethene, ethyne, CO, CH2CHO•, HCO• and methane. In both cases the products are believed to be formed from C—C cleavages of the parent ion followed by hydrogen atom scavenging and/or hydrogen atom abstraction from proximally located species. Dehydrogenation products of propane and ethane are proposed to result from product secondary ionization, a process dependent on high electron currents. Surprisingly, in the case of butanal, the McLafferty Rearrangement, a dominant process in electron ionization mass spectrometry, was not observed to occur. Electron bombardment of acetaldehyde:Ar mixtures produced many decomposition products including methane, CO, HCO•, CH3CO•, CH2CHO•, CH3• and ketene. The isomerization product, vinyl alcohol, was also observed. As way of investigating the mechanisms of the above products, experiments were performed in which the acetaldehyde:Ar mole ratio was varied. Variations in the acetaldehyde:Ar mole ratio produced dramatic variations in the products formed, demonstrating a transition from unimolecular chemistry at low acetaldehyde mole ratios, to processes consistent with bimolecular processes at intermediate mole ratios. Variations in the total flow rate of gas resulted in nonsystematic changes in product yields but provided further evidence for unimolecular methane formation via the elimination of neutral CO. Finally, an investigation into the mechanism of vinyl alcohol using the acetaldehyde isotopomer, CD3CHO, in conjunction with computational methods provided further evidence that enol formation occurs as a result of a direct 1,3-H-transfer and not consecutive 1,2-H-transfers. / Thesis (Master, Chemistry) -- Queen's University, 2009-06-26 10:51:32.331

The amino acid (2S, 4R)-4-hydroxyproline (Hyp) plays a critical role in animal kingdom as structural protein collagen. It is ubiquitous in plant cell walls performing various functions such as structural assembly, plant hormones, plant growth, defense against pathogens, etc. Glycosylation of Hyp is often seen in plant cell walls with L-Arabinofuranose and D-Galactopyranose and not in animal kingdom. Glycosylation is a post-translational modification, which affects characteristics of proteins and peptides. The main objective of this thesis is to synthesize various L-arabinofuranosylated hydroxyproline model amides and investigate their thermodynamic and kinetic properties of cis/trans amide isomerization. These results are compared with the previous research of D-galactopyranosylated hydroxyproline model amides, which may provide an insight to structural implications for their stability and conformations of peptides and specificity in plants. Both - and -L-arabinosylation of Hyp resulted in the stabilization of trans rotameric state at room temperature while the α-anomer leads to cis rotamer stabilization at higher temperature. Similarly, both unnatural 4S-hydroxyproline (hyp) building blocks resulted in stabilization of trans rotamer but α-anomer shows exo configuration instead of endo. This result shows a reverse trend when compared to galactosylated hydroxyproline building blocks as previous research results in our group. Our results may provide further insight to the role of glycosylation on protein structure and stability in plants.