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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.
111

Anellierungsreaktionen zu carbo- und heterocyclischen Ringsystemen - Annelation reactions to carbo- and heterocyclic ringsystems

Stirner, Wolfgang 14 September 2001 (has links)
This work is subdivided in three chapters. In the first chapter the synthesis of a 7,7'-bridged 1,1'-Biisoquinoline by a Pomeranz-Fritsch-Reaction is described. This molecule was seperated in its atropisomers which racemice in solution. The influence of the solvent character to the rate of racemization was investigated. It has been shown that the more polar and the more protic the solvent is the higher is the rate of racemization. The second chapter introduces an easy synthetic route to 6-substituted Benzimidazo[2,1-a]isoquinolines and in the single case of a Furyl-substituent to Isoindolo[2,1-a]quinoxalins. The starting materials, ortho-Alkynyl-substituted Benzaldehydes, are prepared by Sonogashira-Coupling of the Bromobenzaldehydes with different substituted terminal Alkynes. The reaction of o,o'- Bis(phenylethinyl)-substituted Benzil with Hydroxylamine Hydrochloride leads to a rearranged Benzofluorenon. The formation is explained by a domino process including a cyclization-step, a Hetero-Diels-Alder reaction and the final rearrangement. In the third chapter the stereochemical outcome of the McMurry reaction is investigated depending on the length of a tether between the meta and meta'-position of an Bisbenzaldehyde. Only the short dioxapentandiyl tethered Bisbenzaldehyde forms streoselectiv the cis-product. Starting with the dioxaoctandiyl- or dioxatetradecandiyl-tethered Bisbenzaldehydes the thermodynamical more stable trans products are obtained. In a second part the regioselectivity of the oxidative photocyclization of these McMurry-products, leading to tethered Phenathrenes, has been investigated. The dioxapentandiyl- and the dioxaoctandiyl-substituted Stilbenes leads regioselectiv to the 4,5-disubstituted Phenathrenes. Whereas the longer dioxatetradecandiyl-tether allows a change in the product ratio and the 2,5-disubstituted Phenanthrene is obtained as the major product. In all cases no 2,7-Phenanthrene could be detected.
112

Winkelabhängige Streulichtexperimente unter hohen Drücken an Polyethylen/n-Alkan-Systemen - Lightscattering experiments under high pressure at polyethylene/n-alcanesystems

Schicks, Judith Maria geb. Basener 14 September 2001 (has links)
In the theoretical part of this dissertation theintroduction of the thermodynamics of mixtures is followed by the basicknowledge of lightscattering. The correlation between thermodynamics atthe one hand and lightscattering at the other is demonstrated. In the apparativeand practicel part the development, build and handeling of the high pressurecell and the carrying out of the light scattering experiments are shown.In the part "results and discussion" the interesting and partly surprisingresults are presentet and discussed.
113

Darstellung und Reaktionen einiger ß,Y-ungesättigter Ketone - Preparation and reactivity of some ß,Y-unsaturated ketones

Zinovyeva, Lyudmyla 01 October 2003 (has links)
The reactivity of the polycyclic ß,Y-unsaturated ketones under different conditions were investigated. The titled ketons were reacted with Lithiumaluminiumhidrid and Grignard reagents with following dehydratation of the resulted secondary and tertiary alkohol. The Bucherer reaction, thermolysis and photolysis of these ketones were carried out.
114

Ni/Mg/Al catalysts derived from hydrotalcite-type precursors for the partial oxidation of propane - Ni/Mg/Al-Katalysatoren hergestellt aus hydrotalkitartigen Prekursoren für die partielle Oxiadtion von Propan

Schulze, Kai 24 September 2001 (has links)
Ni/Mg/Al containing anionic clays of hydrotalcite-type structure with varying Ni/Mg ratio and constant Al content were synthesised by coprecipitation. Their composition and structure was determined by elemental analysis, XRD, TG-MS and DSC. Their calcination at 700-1000°C resulted in the transformation into the corresponding mixed metal oxides, with their structure depending on the calcination temperature. Temperature programmed reduction/oxidation and high temperature XRD studies were applied to study their reducibility, Ni dispersion and the oxidation of the formed metallic nickel particles. The partial oxidation of propane to syngas could be successfully performed at temperatures between 600 and 900°C over reduced Ni containing catalysts. The conversion of propane and the yield of syngas increased with increasing reaction temperature. The catalysts with a low to medium Ni content exhibited better catalytic performance than those with a higher Ni content or a conventional steam reforming catalyst used as reference. Coking was found to decrease with increasing reaction temperature and to increase with increasing Ni content. Since several factors characterising the catalysts (BET surface area, Mg content and available Ni surface) follow the same or the opposite trend with the Ni content, it was impossible to differentiate between these properties and their effect on the catalyst performance or coking. By the use of the best catalyst an at least two-fold increase in the yield of carbon monoxide and eight-fold increase in the yield of hydrogen was observed compared with the non-catalytic reaction. Further investigations were performed to study the influence of the feed ratio and the space velocity.
115

Polyelektrolyteigenschaften der gelmatrixbildenden Komponenten von Biofilmen - Polyelectrolyte properties of the gel-matrix building components of biofilms

Kenning, Arnd 01 October 2003 (has links)
Goals of this study are to point out strategies to influence the gel-matrix building components of biofilms. One well characterised component of the extracellular polymeric substances (EPS) of the bacterial strain Pseudomonas aeruginosa SG81 is the alginate AlgSG81. AlgSG81 is one main component of EPS and thus of the gel-matrix, too. AlgSG81 is completely dissociated in aqueous solution and therefore a strong polyelectrolyte (PEL). By means of computation with OSF-theory and validation via viscosity measurements the conformation of AlgSG81-chains in aqueous solution at screened and not screened conditions is that of a coil over a large concentration regime. By addition of tetramethylurea (TMU) to aqueous solutions of AlgSG81 the formation of a physical network (gel) is observed. Different empirical and theoretical approaches to characterise PEL were improved and experimental verified.
116

Erstellung und Validierung einer kombinierten NIR/Raman-Bibliothek zur Identitätskontrolle organischer und anorganischer Substanzen - Creation and validation of a combined NIR/Raman-library for identity control of organic and inorganic substances

Mandal, Oliver 02 October 2001 (has links)
Due to legal requests in future the identity control of products will not only be required in pharmaceutical industry but also in chemical industry. Therefore the demands on the analytical methods are very high. The company Merck realized an identity control tool by combining NIR and Raman spectroscopy. This Tool is suited for identification of a broad range of organic and inorganic substances. In this work different chemometric methods and data pretreatments were tested. The NIR and the Raman library have been optimized and the validation results visualized. Alternatives as binary coding and wavelet transformation, which lead to data compression at the same time, were tested
117

Molekulare Mangan-,Eisen- und Cobalt-Komplexe mit neuartigen Metall-Chalcogen-Gerüsten - Molecular manganese-, iron- and cobalt-complexes with novell metal-chalcogenides frameworks

Seidel, Renate Magdalene 10 October 2001 (has links)
The possibility of synthesis of (poly-)chalcogenide and chalcogenolate ions to manganese, iron and cobalt was expanded with the introduction of the donor ligand carbon monoxide. The metal atoms get than greater coordination numbers. So it was possible to synthesise new metal frameworks, p. e. Co11E7 in the complexes [Ph4P]2[Co11Se7(CO)10] and [Ph4P]2[Co11Te7(CO)10], in which the cobalt atoms built a inner centred pentagonal prism. In the examined reaction systems Mn2(CO)10/Na2Sex/Kat, Fe(CO)5/Na2Ex/Kat and Co2(CO)8/Na2Ex/Kat (E = Se or Te; x = 1 or 2; Kat = Ph4PCl or PPNCl) succeeded the synthesis of [Co6Se8(CO)6]-/2-anions as first anionic clusters of the M6E8L6 class. The difference between the new [Co6Se8(CO)4]- anion and the M6E8L6-complex class is the extraordinary compressed Co6-oktaeder and considerable shorter Co-Co-distances. In addition to the higher mentioned compounds it was possible to synthesise and characterize unambiguous with the aid of single crystal x-ray crystallography the following complexes: [Ph4P]2[Fe3Te(CO)9]; [Ph4P][Fe3EH(CO)9] für E=Se,Te; [Ph4P]2 [Fe4Te2(CO)14]; [Ph4P]2 [Fe6Se6(CO)12]; [Ph4P]2 [Mn3Se2(CO)9]. Worth mentioning is also the unusual square pyramidal coordination of the manganese atom in the [Ph4P][Mn(CO)5] crystal. Until now were only penta carbonyl complexes known with a trigonal bipyramidal coordination.
118

Thermodynamische Eigenschaften semirigider Polymere und deren Anwendung in faseroptischen Detektoren - Thermodynamic properties of semirigid polymers and their applications in fibre optical detectors

Woelke, Ralf 12 October 2001 (has links)
In the following thesis the thermotropic phase transition behaviour and structure-property-relations of semiflexible polyesters were investigated. These materials can be used in fibre optical blood-pressure sensors as resonator materials in a Fabry-Perot-Interferometer. PVT-measurements were carried out to determine the thermodynamic parameters alphaV(T) and kappa(P), and the validity of the Ehrenfest equations at glass transition temperatures was verified. These latter investigations showed no thermodynamic second order transition. By using alphaV(T) and kappa(P) for the calculation of the resonator-length-difference, the temperature- and pressure behaviour of the investigated polyesters was simulated. This simulation showed that small variations in the resonator length from increasing pressure agrees with the empirically determined values. An increasing number of methylene groups in the sidechain of the spacer molecule resulted in decreased melting- and glass transition temperature, which revealed the possibility to prepare thin polymer-films with 5-10 micrometer in diameter at low temperatures.
119

Dynamical Behaviour of Small Molecules Clathrated in Syndiotactic Polystyrene: a Solid State Deuterium NMR Investigation - Dynamisches Verhalten kleiner Molekülen innerhalb der Hohlräume von syndiotaktischem Polystyrol: eine Deuterium-Festkörper-NMR-Untersuchung

Trezza, Elena 19 November 2003 (has links)
The crystalline regions of the δ-form of syndiotactic polystyrene (s-PS) contain cavities in which certain small molecules can be absorbed. The mobility of six perdeuterated molecules: benzene, toluene, chloroform dichloromethane, 1,2-dichloroethane and 1,2-dibromoethane, present as a guest in these cavities, has been investigated via 2H NMR spectroscopy. For all samples the motional behavior of the molecules absorbed in the amorphous phase of the polymer differs from that shown by the molecules clathrated in the crystalline phase. The motion of all six molecules in the amorphous phase is approximately isotropic at a temperature T = 298 K or higher, but severely anisotropic when the molecules are included in the crystalline phase. The dynamical behavior of each solvent hosted in the crystalline phase of s-PS has been investigated by comparing spectra obtained by simulation of the effect of a certain molecular rotation on the 2H spectra with the experimental spectra.
120

Verkapselung von organischen Substraten in Polycyanoacrylat-Nanokapseln - Encapsulation of Organic Substrates in Polyalcylcyanoacrylate Nanocapsules

Altinbas, Neslihan 21 November 2003 (has links)
In this work, nanocapsules were synthesized from n-butylcyanoacrylat (BCA) and characterized under variation of kind and quantity of the synthesis components. The influences of the quantity variations were interpreted, using a reduced and a complete factorized experimental design. Hereby, the properties of the capsules have been specified, such as width, width distribution, density, wall thickness and morphology of the capsule. For the verification of the construction of the capsules and their characterization different analytical methods have been used, i.e. TGA, TEM, AFM, AUZ and DLS. In addition, Zeta potentials have been measured and taken into consideration.

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