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The Global ETD Search service is a free service for researchers
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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.
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Showing 61 to 66 of 66 (0.056 seconds)| 61 |
Development of the Solution-Spray Flash-Vacuum-Pyrolysis Technique in the Synthesis of Allenyl Isothiocyanates and Synthesis of Complex 2-Amino-1,3-thiazole DerivativesRichter, Frank 29 June 2015 (has links)
Gas-phase thermolysis is a long-known and well established method for the preparation of reactive species. It is, however, limited to relatively volatile substances, which are easily vaporised. In the present work, the solution-spray technique for preparative scale was developed. With this technique, it is possible to subject low-volatile substances, which hardly vaporise even under high-vacuum conditions, to gas-phase thermolysis. By utilising oil nozzles used in heating and burner systems, it was possible to integrate a stable solution-spray into the existing flash-vacuum-pyrolysis system. The influence of several variables, such as flow-rate, pressure, temperature and solvent was determined. The solution-spray technique was applied in [3,3]-sigmatropic rearrangements of certain propargyl thiocyanates to the corresponding allenyl isothiocyanates.
Furthermore, the parent compound propa-1,2-dienyl isothiocyanate was reacted with various sterically demanding primary and secondary amines to form 2-amino-1,3-thiazoles in moderate to excellent yields. Based on this, a catalyst-free four-center three-component reaction was developed. 2-Amino-1,3-thiazoles with complex substituents in 5-position at the heterocyclic ring are formed. Reaction mechanisms are discussed to explain the occurance of a highly substituted 1,3-thiazine structure. The influence of reaction temperature, concentrations and solvent were determined and are also discussed.
It was shown that 2-amino-5-methyl-1,3-thiazoles are the apparently first aromatic substance class, that readily undergoes Prins-type 1,3-dioxane ring-formation. / Die Gasphasenthermolyse ist eine lang bekannte und etablierte Methodik zur Synthese reaktiver Spezies. Sie ist allerdings auf flüchtige Substanzen mit einer guten Verdampfbarkeit beschränkt. Für schwerflüchtige Verbindungen, welche sich selbst im Hochvakuum nur mäßig oder gar nicht in die Gasphase bringen lassen, wurde in der vorliegenden Arbeit die Solution-Spray-Technik für die Anwendung im präparativen Maßstab entwickelt. Unter Verwendung von Ölzerstäuberdüsen, wie sie in der Heizungs- und Brennertechnik Anwendung finden, wurde die Erzeugung eines stabilen Lösungs-Sprays in die vorhandene Blitzvakuumpyrolyse-Technik integriert. Der Einfluss verschiedener Variablen, wie Flussrate, Druck, Temperatur und Lösungsmittel wurde untersucht. Die Solution-Spray-Technik wurde für die [3,3]-sigmatrope Umlagerung bestimmter Propargylthiocyanate zu Allenyl-isothiocyanaten angewendet.
Des Weiteren wurde Propa-1,2-dienylisothiocyanat – das einfachste Allenylisothiocyanat – mit diversen sterisch anspruchsvollen primären und sekundären Aminen in mäßigen bis exzellenten Ausbeuten zu 2-Amino-1,3-thiazolen umgesetzt. Darauf aufbauend konnte eine Vier-Zentren-drei-Komponenten-Reaktion entwickelt werden. Es entstehen in hohen Ausbeuten 2-Amino-1,3-thiazole mit komplexen Substituenten an der 5-Position des Heterocyclus. Reaktionsmechanismen werden diskutiert um die alternative Bildung einer hochsubstituierten 1,3-Thiazinstruktur zu erklären. Der Einfluss von Reaktionstemperatur, Konzentration und Lösungsmittel auf das Produktverhältnis wurde ebenfalls untersucht und wird diskutiert.
Es konnte gezeigt werden, dass 2-Amino-5-methyl-1,3-thiazole als offenbar erste aromatische Substanzklasse sehr gute Substrate für die Bildung von 1,3-Dioxanen nach Prins darstellen.
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Strategies for Computational Investigation of Reaction Mechanisms in Organic and Polymer Chemistry Using Static Quantum MechanicsTchernook, Ivan 03 March 2016 (has links) (PDF)
This thesis presents computational studies of problems in the organic and polymer chemistry. The state-of-the art quantum chemical methods are used to gain further insight into the origin and the nature of the reactions in three different organic and polymer systems. The research questions are conceptually approached by identifying the key aspects. Then an appropriate strategy for the quantum chemical modeling is developed.
In the scope of the polymer chemistry, the novel synthesis technique of nanostructured materials, the so-called twin polymerization, is investigated. Using three model systems of increasing complexity the influence of the anion (trifluoroacetate) in the reaction system is investigated. The effect of the solvent polarity as well as the effect of the entropic contributions are also considered.
The rearrangement reaction of the volatile cyanotritylcarbenes is another topic. These carbenes readily rearrange to ethene main products, however also small amount of the unexpected heptafulvenes is formed. This unprecedented heptafulvene formation is modeled in detail and the energetics is systematically evaluated to identify most reasonable rearrangement pathways of the probable multiple alternative routes. Computational investigation of other tritylcarbenes with varying spectator substituents results in sophisticated data base for experimental investigations.
At last, some controversial observations in experimental studies concerning the kinetics of the electrophilic alkylation of the barbiturate anion are studied. To interpret the kinetic measurements, different alkylation pathways are analyzed with respect to their energetics. Further, the influence of microsolvation is demonstrated.
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Enantioselektive Darstellung bioaktiver FlavanoneWitt, Morris 01 July 2014 (has links) (PDF)
Diese Dissertation beschreibt die Synthese der vier Flavanone Lonchocarpol A, 6-Dimethylallylnaringenin, Glabrol und Euchrenon A7. Des weiteren konnten drei dieser Naturstoffe enantiomerenrein mit Hilfe einer kinetischen Racematspaltung hergestellt werden. Dabei wurden die Carboxylkohlenstoffe selektiv mit einer asymmetrischen Transferhydrierung nach Noyori reduziert.
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Enantioselektive Darstellung bioaktiver FlavanoneWitt, Morris 15 January 2014 (has links)
Diese Dissertation beschreibt die Synthese der vier Flavanone Lonchocarpol A, 6-Dimethylallylnaringenin, Glabrol und Euchrenon A7. Des weiteren konnten drei dieser Naturstoffe enantiomerenrein mit Hilfe einer kinetischen Racematspaltung hergestellt werden. Dabei wurden die Carboxylkohlenstoffe selektiv mit einer asymmetrischen Transferhydrierung nach Noyori reduziert.
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Strategies for Computational Investigation of Reaction Mechanisms in Organic and Polymer Chemistry Using Static Quantum MechanicsTchernook, Ivan 12 February 2016 (has links)
This thesis presents computational studies of problems in the organic and polymer chemistry. The state-of-the art quantum chemical methods are used to gain further insight into the origin and the nature of the reactions in three different organic and polymer systems. The research questions are conceptually approached by identifying the key aspects. Then an appropriate strategy for the quantum chemical modeling is developed.
In the scope of the polymer chemistry, the novel synthesis technique of nanostructured materials, the so-called twin polymerization, is investigated. Using three model systems of increasing complexity the influence of the anion (trifluoroacetate) in the reaction system is investigated. The effect of the solvent polarity as well as the effect of the entropic contributions are also considered.
The rearrangement reaction of the volatile cyanotritylcarbenes is another topic. These carbenes readily rearrange to ethene main products, however also small amount of the unexpected heptafulvenes is formed. This unprecedented heptafulvene formation is modeled in detail and the energetics is systematically evaluated to identify most reasonable rearrangement pathways of the probable multiple alternative routes. Computational investigation of other tritylcarbenes with varying spectator substituents results in sophisticated data base for experimental investigations.
At last, some controversial observations in experimental studies concerning the kinetics of the electrophilic alkylation of the barbiturate anion are studied. To interpret the kinetic measurements, different alkylation pathways are analyzed with respect to their energetics. Further, the influence of microsolvation is demonstrated.
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Die Iromycine und das Collinolacton: Synthese mikrobieller Naturstoffe aus Streptomyces sp. / The Iromycins and the Collinolacton: synthesis microbial natural products from Streptomyces sp.Shojaei, Heydar 02 May 2007 (has links)
No description available.
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