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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Enatioselective nucleophillic catalysis with [2.2]paracyclophane-based heterocycles

Hodgson, Andrew January 2008 (has links)
This thesis is concerned with understanding and further developing the chemistry of [2.2]paracyclophane, and is divided into three main sections. The first section is a review of the methods to synthesize aryl substituted [2.2]paracyclophanes. This is followed by a discussion section focusing on the development of planar chiral [2.2]paracyclophane based triazolium salts, DMAP and benzimidazole derivatives, and their potential applications as enantioselective nucleophilic organocatalysts.
92

Synthesis, characterisation and properties of benzenepolycarboxylate metal-orgnanic frameworks

Holcroft, James Matthew January 2012 (has links)
Metal-organic frameworks (MOFs) are coordination polymers that extend in one, two or three dimensions, forming networks. These materials need to be strongly bonding metal centres linked by organic ligands to form a geometrically well-defined structure. MOFs are of interest due to our ability to identify some of the principles that govern the design and assembly of the target framework. The careful selection of MOF building blocks such that their properties are retained by the framework can yield unique materials with a host of physical characteristics and applications. The nature of the organic linkers often leads to voids present in the structure; these are usually occupied by guest molecules such as solvent, which need to be removed or exchanged for the MOF to be activated. The design of frameworks that are robust and withstand the desolvation can lead to porous compounds with the ability to adsorb other guest molecules, giving a platform for numerous scientific and industrial applications. This thesis describes the synthesis, the structural characterisation and the study of thermostability and gas adsorption characteristics of MOFs. The structures of compounds of some transition metal ions [Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)] and some other metals with symmetrical benzenepolycarboxylates (terephthalic, trimesic, pyromellitic and mellitic acid) are described. A detailed adsorption study of one particular compound is presented. The compounds presented were prepared using a variety of methods: solvothermal, hydrothemal, ionothermal, vapour diffusion and solvent diffusion using specially adapted reaction vessels. Single-crystal X-ray crystallographic techniques were used for structure determination and characterisation, utilising in-house and synchrotron facilities. Further analysis was carried out using elemental analysis and powder X-ray diffraction to determine overall „bulk‟ sample purity. Thermogravimetric analysis and hot-stage microscopy were used to assess the thermal stability of selected compounds, producing the temperature profile needed for Intelligent Gravimetric Analysis which determined the pore characteristics and potential applications of the compounds. A total of forty-four metal–benzenepolycarboxylate complexes are presented, mostly with transition metals. Nine complexes containing the 1,4-benzenedicarboxylate ligand (terephthalate) (1-9) are reported. This ligand formed complexes with zinc (3,5,6,8), cobalt (2,4), nickel (1), cadmium (7) and copper (9). The structures of the compounds include one-dimensional chains (1,2), two-dimensional sheets (3-6) and three-dimensional coordinated frameworks (7-9). Twelve complexes containing the 1,3,5-benzenetricarboxylate ligand (trimesate) (10-21) are reported. This ligand formed complexes with zinc (11,12,17), cobalt (14,18), nickel (13), cadmium (15,16) and manganese (19,10,21). The structures of the compounds include two-dimensional sheets (10-12,16) and three-dimensional coordinated frameworks (17-21). Fifteen complexes containing the 1,2,4,5-benzenetetracarboxylate ligand (pyromellitate) (22-36) are reported. This ligand formed complexes with zinc (32,33,36), cobalt (22,25,34,35), nickel (26), cadmium (27,28,31), copper (23,24,29) and the alkali metal potassium (34). The structures of the compounds include two-dimensional sheets (22-27) and three-dimensional coordinated frameworks (28-36). Eight complexes containing the fully substituted 1,2,3,4,5,6-benzenehexacarboxylate ligand (mellitate) (37-44) are reported. This ligand formed complexes with cobalt (41), nickel (37,38), cadmium (42,43), copper (39,40,44). The structures of the compounds include one-dimensional chains (37), two-dimensional sheets (39,41,42) and three-dimensional coordinated frameworks (38,40,43,44). The adsorption characteristics of the porous MOF NEW105 (compound 17) were studied. N2 and CO2 adsorption at low temperatures gave a pore volume that was much lower than the value calculated from the crystallographic data. Virial analysis of the CO2 isotherm confirmed interactions that are equivalent to ultra-nanoporous materials, indicating that the structure has undergone a structural rearrangement. Further kinetic analysis of gas adsorption isotherms of CO2, N2 and O2 showed the new nanoporous material was capable of kinetic molecular sieving of gases, a process observed only once before in MOFs. The Adsorption studies were carried out by Northern Carbon Research Laboratories; M. Thomas, J. Bell and J. Armstrong.
93

Synthesis of some aromatic hydrocarbons

Houlton, Peter Robert January 1968 (has links)
No description available.
94

An investigation of intumescent pyrotechnics : synthetic studies towards FK506 and morphine

Shell, Adrian January 1996 (has links)
No description available.
95

An investigation of the structural chemical and electrical conduction properties of metal atom chain compounds

Wood, D. J. January 1981 (has links)
No description available.
96

Application of segmented flow technique in catalytic organic syntheses

Omer, Batoul Ahmed January 2008 (has links)
Microflow technology has become an innovative and fashionable tool in synthetic organic chemistry, opening the way to novel challenging interactions between chemistry and other scientific disciplines. The system properties and reaction conditions in microflow chemistry are different to those in flask as a result of higher surface-to- volume ratios and shorter diffusion distances bringing significant advantages over conventional flask method such as improved heat transfer and reduced mixing times. More and more multiphase microflow systems have begun to emerge over the last few years, offering a variety of methodologies. The attention to the various emerging microflow techniques represented the starting point for the development of the present work. The study presented in this thesis focuses on the application of microflow systems using segmented flow technique to various organic transformations by development of a practical and economical system setup in order to provide a basic methodology for synthetic chemists. First, we carried a comparison study between microflow and flask reaction using a simple biphasic hydrolysis under segmented flow. The study was then extended to investigate the effect of parallel vs. segmented flow, in addition to the variation of reaction parameters in the microflow system, such as heating, sonication, and microchannel size. We selected for our study two classes of catalytic organic reactions of particular synthetic relevance, namely palladium-catalysed Heck coupling and ruthenium-catalysed ring-closing metathesis. We carried out biphasic Heck catalysis then moved onto the study of segmented flow application to monophasic reactions both in single step and multistep syntheses. Overall the use of microflow technique, applied to a number of reactions of various types and carried out with many chemical and engineering variables, allowed us to observe overall reaction performances enhancement compared to conventional flask chemistry, on the whole rather agreeably, reproducibly, and displaying very regular trends.
97

Some reactions of phosphorus compounds as studied by ³¹P NMR techniques

Nisbet, M. P. January 1967 (has links)
The solution chemistry of some simple phosphorus halides has been investigated in sulphuric acid, oleums, and halo-substituted sulphuric acids by (^31) p n.m.r. spectroscopy. Solution of phosphorus (III) compounds was accompanied by oxidation to the phosphorus (V) state. The phosphorus (V) species so formed as well as those derived directly from phosphorus (V) halides and oxyhalides were stable over measurable periods of time. Solvolysis of phosphorus (V) – halogen bonds occurred in all the solvents, with some complications arising in the halo-substituted acids where halogen exchange was observed. Oxidation of some phosphorus (III) halides by halogens produced phosphorus (V) - halo species which were stabilized by solution in these highly acidic solvents. The (^31) p n.m.r. solution spectrum of various phosphorus (V) - iodine species have been recorded for the first time with the help of a pulsed Fourier Transform instrument capable of studying reacting systems. The solution chemistry of a series of phenyl organophosphoryl compounds in these acid solvents has also been investigated by (^31) P n.m.r. Protonation of the phosphoryl group takes place in all of the solvents, as well as sulphonation of the phenyl ring in 25% and 65% oleum, and to a lesser extent in ClHSO (_3). Mixed halo and organohalo phosphorus (V) compounds such as [PCl (_N) Br (_4-n)] (^+) A (^-), R (_N) PX (_5-n), [R (_n) PX (_4-n)] (^+) A (^-), where X = Cl or Br and A (^-) is an anion, dissolve in 25% oleum with the formation of stable phosphonium cations. An investigation of the solution chemistry of phenoxyhalophosphoranes indicates that the stable species in the system are the non halo containing (PhO) (_4) p (^+) cation and (PhO) (_5) P, neither of which show acceptor properties towards pyridine or chloride ions. A limited investigation of the Lewis acid properties of PI (_3) towards pyridines and the Lewis base properties of PI (_3) towards BBr (_3) and BIr (_3) suggests that coordination complexes are formed in both systems. Oxidation of PI (_3) has been attempted by means of halogens and other halogen-containing oxidizing agents. No direct evidence for the formation of phosphorus (V)-iodine species was obtained, although reactions with SbCl (_5) and PCl (_5) produced unstable compounds which decomposed at low temperature liberating iodine.
98

Theoretical aspects of structure bonding and reactivity of some unsaturated organic systems

Scanlan, Ian William January 1974 (has links)
No description available.
99

A study of addition products of fluorocarbon olefins

Kisby, Jill January 1964 (has links)
No description available.
100

Solvolytic studies of organic sulphonates

Tidy, D. January 1964 (has links)
This thesis describes a kinetic study of the hydrolysis of alkyl and aralkyl esters of toluenesulphonic acid in aqueous acetone The information available at the beginning of the present work suggested that these reactions can be regarded as nucleophilic substitution reactions but there was no certainty about the unimolecular mechanism, S(_N)l. The determination of the activation parameters for the hydrolysis of compounds which can be expected to react either by mechanism S(_N)l or by mechanism S(_N)2 showed that mechanistic tests based on the ratio of the heat capacity of activation to the entropy of activation (Bensley and Kohnstam, J.C.S. 1957, 4747.) could be applied to sulphonates as well as to halides. The application of this test to the hydrolysis of p-substltuted benzyl toluenesulphonates showed that only p-substituents which were better electron-donors than the methyl group gave reaction entirely by mechanism S(_N)l. Anions which are more powerful nucleophiles than water gave some bimolecular reaction with the substrate even when hydrolysis occurred unimolecularly and bimoleoularly reaction was observed between hydroxide ions -and benzyl toluenesulphonate, in contradiction to some earlier reports. Changes in the composition of the solvent only have small effect on the reaction mechanism, though the hydrolysis of i-propyl toluenesulphonate was found to occur entirely by mechanism S(_N)l in "50%" aqueous acetone, but not in the "85%" solvent. Comparison of the activation parameters for the hydrolysis of toluenesulphonates and the corresponding halides shows that a significant part of the greater reactivity of the sulphonates results from the more favourable entropy of activation. It is considered that this arises from the fact that sulphonates require less additional solvation by water on activation than the halid.es.

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