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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.
481

Aluminium triflate as a Lewis acid catalyst in some epoxide and aromatic transformations

Lawton, Michelle Claire 14 March 2012 (has links)
M.Sc. / Lewis acids play an important role in catalysis; they are associated with mild conditions, high selectivities and unique reactivities. Traditional Lewis acids such as AlCb and BF3 successfully catalyse such well known reactions as the Friedel-Crafts acylation reaction, Aldol condensation reactions and many more. These catalysts, however, must be used in a stoichiometric amount and are destroyed during the aqueous workup procedures. Lately, there has been a lot of interest in the role of metal triflate as Lewis acid catalysts. They were found to be effective in a wide range of reactions when used in catalytic amounts. They were also found to be recyclable and reusable without the loss of activity. Most of this research has been centred around the lanthanide triflates as well as scandium, bismuth and yttrium triflates. Very little research has been done using aluminium triflate and this triflate forms the focus ofthis study. The work contained in this dissertation demonstrates that Al(OTf)3 is an efficient catalyst for the ring opening of a variety of epoxides by alcohols when present in only ppm amounts. These reactions provided products in very high yields and selectivities. Simple acyclic and cyclic epoxides readily underwent ring opening reactions with a range of alcohols, typically providing the monoglycol ethers as single compounds (from the cyclic epoxides) or as mixtures of the two possible glycol monoethers (from the acyclic epoxides). In the case of styrene oxide, essentially a single compound was isolated. In contrast, the glycidyl ethers required slightly higher catalyst loadings before similar rates and conversions to product were observed. Additionally, an interesting selectivity was observed in the orientation of the attack of the alcohol onto the epoxide, which appeared to be chelation controlled. Similarly, the Al(OTf)3 also catalysed the aminolysis of a variety of epoxides. These reactions proceeded smoothly with catalytic amounts of the triflate present, and served to nicely highlight the role that steric and electronic factors played in these reactions. A preliminary study was carried out into the efficacy of Al(OTf)3 as a catalyst for Friedel-Crafts acylation and aromatic nitration reactions. From these studies it is evident that the Al(OTf)3 is indeed an effective catalyst for these reactions when present in substoichiometric levels and further studies will be carried out in this area in the future.
482

Lewis, counterfactual analyses of causation, and pre-emption cases

Landsberg, David January 2009 (has links)
Over the past few decades analyses of causation have proliferated in almost immeasurable abundance, and with two things in common; firstly, they make much of counterfactual dependence, and secondly, none of them successfully handle all the pre-emption cases. In this thesis, I fore-mostly investigate David Lewis’ promising counterfactual analyses of causation (along with many others), and provide an extensive examination of pre-emption cases. I also offer my own counterfactual analysis of causation, which I argue can handle the problematic pre-emption cases, and therein succeed where so many other prominent analyses of causation have failed. I then conclude with some morals for the continuing debate.
483

Catalyse au fer : synthèse de 2H-chromènes, synthèse de métachromines / Iron catalysis : synthesis of 2H-chromenes, synthesis of metachromins

Calmus, Laurent 14 November 2014 (has links)
La mise au point de nouvelles méthodes de synthèse permettant d'accéder à des produits biologiquement actifs en utilisant réactifs peu onéreux dans des conditions respectueuses de l'environnement est un enjeu majeur. Le motif 2H-chromène est présent dans un grand nombre de molécules naturelles, et notamment dans plusieurs métachromines. Les métachromines sont des méroterpénoïdes naturels possédant des propriétés biologiques intéressantes. Notre étude s'est portée sur le développement d'une méthode de synthèse permettant d'accéder à des 2H-chromènes hautement fonctionnalisés par une réaction de cyclisation catalysée par des complexes de fer(III) à partir d'alcools allyliques phénoliques ainsi que l'application de cette méthode à la synthèse de produits naturels.Dans une première partie, cette méthode a été appliquée à des alcools allyliques phénoliques mono-, di-, tri-, ou tétra-substitués, pour conduire aux 2H-chromènes de manière efficace. L'étude de cette méthode a montré qu'un grand nombre de fonctionnalités étaient tolérées et qu'il était possible de moduler la réactivité des alcools allyliques phénoliques par la substitution du cycle aromatique et de la double liaison allylique. Cette méthode a été utilisée efficacement comme étape-clé dans la première synthèse totale de la téphrowatsine B, un 2H-chromène naturel issu d'une plante équatoriale présentant des propriétés insecticides. Dans une seconde partie, la première synthèse totale des métachromines J et T a été abordée. Notre méthode a été utilisée comme étape-clé pour accéder à un fragment 2H-chromène, précurseur commun de ces molécules. La synthèse totale de la métachromine C a également été étudiée. / The development of new synthetic methods, which could be used in the synthesis of biologically active compounds using inexpensive reactants and environmentally friendly conditions, is a major challenge in modern chemistry. 2H-Chromenes are present in a large number of biologically active compounds and especially in metachromins. Metachromins are natural marine meroterpenoids that present interesting biological activities. With these objectives in mind, our investigations were focused on the development of a synthetic method to access highly functionalised 2H-chromenes from readily accessible phenolic allylic alcohols, catalysed by iron(III) complexes as well as applications to the synthesis of various natural products. At the beginning, this method was applied to mono-, di-, tri- and tetra-substituted phenolic allylic alcohols to efficiently access the corresponding 2H-chromenes. This method tolerated a large number of functionalities and it was possible to modulate the reactivity of the substrates by substituting the aromatic ring and/or the allylic double bond. This method was applied as a key step in the first total synthesis of tephrowatsin B, a natural 2H-chromene isolated from an equatorial plant having insecticidal activities. On the other hand, the first total synthesis of metachromin J and T was investigated. Our method was used as a key step to access their 2H-chromene fragment, a common precursor of these molecules. The total synthesis of metachromin C was also studied.
484

Direct Catalytic Nucleophilic Substitution of Non-Derivatized Alcohols

Bunrit, Anon January 2017 (has links)
This thesis focuses on the development of methods for the activation of the hydroxyl group in non-derivatized alcohols in substitution reactions. The thesis is divided into two parts, describing three different catalytic systems. The first part of the thesis (Chapter 2) describes nucleophilic allylation of amines with allylic alcohols, using a palladium catalyst to generate unsymmetrical diallylated amines. The corresponding amines were further transformed by a one-pot ring-closing metathesis and aromatization reaction to afford β-substituted pyrroles with linear and branched alkyl, benzyl, and aryl groups in overall moderate to good yields. The second part (Chapters 3 and 4) describes the direct intramolecular stereospecific nucleophilic substitution of the hydroxyl group in enantioenriched alcohols by Lewis acid and Brønsted acid/base catalysis. In Chapter 3, the direct intramolecular substitution of non-derivatized alcohols has been developed using Fe(OTf)3 as catalyst. The hydroxyl groups of aryl, allyl, and alkyl alcohols were substituted by the attack of O- and N-centered nucleophiles, to provide five- and six-membered heterocycles in up to excellent yields with high enantiospecificities. Experimental studies showed that the reaction follows first-order dependence with respect to the catalyst, the internal nucleophile, and the internal electrophile of the substrate. Competition and catalyst-substrate interaction experiments demonstrated that this transformation proceeds via an SN2-type reaction pathway. In Chapter 4, a Brønsted acid/base catalyzed intramolecular substitution of non-derivatized alcohols was developed. The direct intramolecular and stereospecific substitution of different alcohols was successfully catalyzed by phosphinic acid (H3PO2). The hydroxyl groups of aryl, allyl, propargyl, and alkyl alcohols were substituted by O-, N-, and S-centered nucleophiles to generate five- and six-membered heterocycles in good to excellent yields with high enantiospecificities. Mechanistic studies (both experiments and density functional theory calculations) have been performed on the reaction forming five-membered heterocyclic compounds. Experimental studies showed that phosphinic acid does not promote SN1 reactivity. Rate-order determination indicated that the reaction follows first-order dependence with respect to the catalyst, the internal nucleophile, and the internal electrophile. DFT calculations corroborated with a reaction pathway in which the phosphinic acid has a dual activation mode and operates as a bifunctional Brønsted acid/Brønsted base to simultaneously activate both the nucleophile and nucleofuge, resulting in a unique bridging transition state in an SN2-type reaction mechanism. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.</p>
485

Varför frigörelse för djuren? : En jämförande analys mellan Lewis Gompertz och Peter Singers djuretiska tänkande / Why liberation for the animals? : A comparative analysis of the animal ethical thoughts of Lewis Gompertz and Peter Singer

Lehto, Magnus January 2017 (has links)
This study examines differences and similarities in how two animal ethicists living in different times have argued for a liberation of the animals, the basis for the study is Lewis Gompertz Moral Inquiries: On the Situation of Man and of Brutes (1824) and Peter Singers Animal Liberation (1975). The analysis has been conducted with a historical perspective where close reading and contextualization have been used to further understand both the sources and the authors. The investigation is limited to four themes: animal's ability to experience, to kill animals, using animals and products of animals, and finally the idea of equality. The study concludes that there are significant similarities between the arguments Gompertz and Singer use, and that their ideas are rooted in a view of equality where the ability to suffer and have needs should be fundamental for our moral caring towards other creatures. A significant difference between the authors is their relationship to reason, where Gompertz highlights the animals' ability to reason as a cause to treat them well while Singer dismisses the idea that such abilities are of any interest for our moral considerations. The study also points out that the differences in the authors' conclusions and arguments can be understood on the basis of the scientific and intellectual context they operate in, where Gompertz can be described as an enlightenment philosopher with a strong belief in the developable reason within creatures, while the modern-day philosopher Singer rather sees reason as excluding, not only of animals but also of human beings. For animals to be liberated from man's oppression, both writers argue that it is necessary for man to eat a vegetarian diet.
486

Face to face with the Lewis Chessmen : an exploration of children's engagement with material heritage at the National Museum of Scotland

Bull, Nicola Lucy January 2014 (has links)
Museums can be productive sites for the study of society, because they are spaces where the constitution of knowledge about the past is made visible through public display. Playing an important role in the performance and legitimisation of national culture, museums in Scotland pay particular attention to the education of children. It is often claimed that children can gain an understanding of their history through physical engagement with museum collections. Both the ‘past’ and the ‘future’ are thus constituted within the museum. Through an exploration of children’s education at the National Museum of Scotland and The Lewis Chessmen: Unmasked touring exhibition, I argue that efforts by museums to exert control over ongoing processes through which subjects and objects, past and future, nations and heritage are constituted can be deeply challenged by children and museum objects, both of whose status remain inherently dynamic and unstable. Despite the museum’s claims to have “real things [objects] revealing stories”, objects rarely reveal narratives beyond those exerted upon them. They are, instead, materially and relationally constituted in particular places, at particular times. The same ‘instability’ applies to children visiting the museum. Children engage with the material stuff of the museum in surprising and unpredictable ways. This dynamic, multisensory interaction enables children to pursue personal projects, which do not necessarily adhere to the agendas of the museum. Yet, children often do go along with the museum’s narratives, commonly accepting what they are told by adults about the objects they are handling. They are also deeply concerned with the authenticity of these objects. Whether an objects is ‘real’ or not, however, is not necessarily judged by the same standards shared with the museum. Children’s awareness of a ‘real’ object’s metonymical presence not only enables an experiential encounter with the past, but also enables them to work out their own positions within the power structures of the museum; testing their own concerns relating to trust, truth, value and the process of becoming adults.
487

En strukturell resa genom Narnia : -    En komparativ analys av struktur och genre i C.S Lewis två verkSilvertronen och Hästen och hans pojke

Hänninen, Linnéa January 2017 (has links)
En strukturell resa genom Narnia: En komparativ analys av struktur och genre i C.S Lewis två verk Silvertronen och Hästen och hans pojke A structural trip through Narnia: A comparative analysis of structure and genre in C.S Lewis two works The Silver Chair and The Horse and His Boy In this essay I discuss how fiction can be used in Swedish education for younger years in the Swedish subject, to learn about the building blocks of stories and what is unique to the fantasy genre. The core of the essay is an analysis of C.S Lewis two novels The Silver Chair and The Horse and His Boy and how they relate to some of Vladimir Propps 31 functions of structures and some characteristics of the genre fantasy. The purpose of this essay is examine how the two works of C.S Lewis relate to chosen functions, characterises of the genre fantasy and in relation to each other. That and how it can be used in Swedish education to create an interest for fiction and reading. The analysis is built on two parts. Firstly, the two books are introduced and then analysed separately against 10 of Propps functions and described characteristics of the genre fantasy. Secondly, a comparison between the result from the two separate analyses. I find that fiction can be compared to both Propp’s functions and characteristics of the genre fantasy. However, they needed to be interpreted to fit into the definitions of chosen functions. As a result, I found that the fictions by C.S Lewis, Propps functions and elements of the fantasy genre can be used in classrooms to discuss the structure of stories and to teach about genres. I also give some ideas on how to do that.
488

Applications of metal triflates and assisted acids as catalysts for organic transformations

Sibiya, Mike Sbonelo 05 November 2012 (has links)
Ph.D. / The research contained in this thesis was aimed at the applications of Lewis acids (metal triflate salts in particular) and Brønsted acids as catalysts for various organic synthesis reactions. The ultimate objective was to prepare combinations of the Lewis and Brønsted acids to form assisted acids. The assisted acids yield to the formation of highly acidic assisted acids which exhibit high activity as compared to the individual Lewis and Brønsted acids. A detailed literature study was undertaken, with emphasis on the applications of metal triflate salts as catalysts for various organic reactions and the applications of assisted acids. The study was motivated by the fact that metal triflate Lewis acids are thermally stable, non corrosive and water tolerant catalysts, hence can be used industrially to replace the corrosive, moisture sensitive acids as catalysts. However, metal triflates have not yet been recognised and utilised in the chemical industry. On the other hand, the active Brønsted acids such as triflic acid, H2SO4 etc. are corrosive, which restricts the type of construction material to hastelloy. However, the assisted acids composed of less corrosive Brønsted acids and metal triflate Lewis acid is desirable to address the corrosion and safety challenges. The metal triflate salts and Brønsted acids were evaluated as catalysts for etherification reactions of alcohols and olefins, Friedel-Crafts alkylation reactions phenolic substrates with isobutylene. The study showed that some dependence of the charge density to the activity, i.e. metal triflate salts such as Al(OTf)3, Zr(OTf)4 and Sc(OTf)3 with relatively high charge density were more effective in catalysing the reactions than those with relatively smaller charge density such as lanthanides, which were virtually active. The activity of Brønsted acids showed a clear dependence on the acid strength pKa, with H3PO4 giving the least activity. The assisted acids formed via a combination of metal triflate salts with mineral Brønsted acids showed a significant enhancement of the reaction rates as compared to the individual acids. This set of new combined acids was proven to be excellent catalysts for the etherification reactions, Friedel-Crafts alkylation reactions and also for the synthesis of biologically active compounds called chromans. The assisted acids as well as Al(OTf)3, and Zr(OTf)4 could be recycled at least four times without significant loss of activity. The study also showed that assisted acids could be recycled for both etherification and Friedel-Crafts reactions.
489

The metaphysics of privileged properties

Wilson, Aaron January 2016 (has links)
Objects are characterised by their properties. If an object is a red postbox, then it has the property of being red, and the property of being a postbox. This thesis is an attack on a particular view of the metaphysics of properties, according to which some properties are privileged over others. The most well-known theories of privileged properties are Armstrong’s theory of sparse immanent universals (1979b) and Lewis’ natural properties (1983). According to their supporters, only privileged properties perform certain jobs, such as featuring in laws of nature, or grounding similarity between objects. Metaphysical posits are theoretically virtuous if they can account for a range of different phenomena in a relatively parsimonious manner. The ability of privileged properties to perform a range of worthwhile ‘work’, therefore, is what justifies a belief in them. The conclusion I reach is that a single group of properties is not capable of satisfying the key roles commonly attributed to the privileged properties. Without satisfying these roles in concert, a belief in mainstream versions of privileged properties is not justified. The first part of this thesis is devoted to an explication of privilege and the roles which privileged properties are taken to perform. I conclude that three roles in particular, Supervenience, Similarity and Magnetism are key roles for mainstream theories of privilege. In part two, I show that the properties which satisfy the Supervenience role are not the same as those which satisfy the Similarity and Magnetism roles. In the final chapter of this thesis I discuss the implications of my findings for support for theories of privilege.
490

Geochemistry of the Ultramafic Rocks from the Bay of Island Ophiolitic Complex, Newfoundland.

Stern, Fabio G. January 2013 (has links)
The Bay of Islands Ophiolitic Complex (BOIC) is one of most well preserved and well-exposed ophiolites in the world. The BOIC consist of four massifs; these are the Table Mountain (TBL), North Arm Mountain (NAM), Blow-Me-Down Mountain (BMD) and Lewis Hills massifs. Proposed geological environments of the BOIC in Newfoundland are diverse; ranging from oceanic spreading ridge to supra-subduction setting. The BOIC has a complete ophiolite sequence as defined at the Penrose Conference (Anonymous, 1972) including ultramafic mantle rocks, ultramafic to gabbroic cumulate rocks, sheeted dikes, pillowed basaltic rocks and capping sedimentary rocks in structurally ascending order. We studied harzburgite and overlying massive dunite in the BOIC. Harzburgite is generally medium-grained, and contains olivine, orthopyroxene, Cr-spinel, clinopyroxene and rare sulfide minerals. Harzburgite is massive to strongly deformed, with local development of mylonitic shear zones. A foliation and lineation are defined by elongated and fragmented grains of orthopyroxene and Cr-spinel. Dikes, sills, veins, and irregularly-shaped bodies of dunite and pyroxenite are present throughout the harzburgite unit. Dunite is the predominant lithology of the Blow-Me-Down Mountain. It is typically fine- to medium-grained, massive, and contains minor Cr-spinel and rare sulfide minerals. Dunite contains olivine, Cr-spinel and minor pyroxenes in some samples. Olivine crystals are commonly partly replaced by serpentine along fractures and in outer rims. Bulk rock and mineral composition data suggest that harzburgites are mild to highly refractory mantle residues after partial melting. In contrast all dunite samples show a cumulate geochemical signature from a mafic melt that originated from highly refractory mantle peridotites. Our study suggest that the harzburgite in the BOIC originally formed as oceanic lithosphere at a slow spreading ridge, possibly in the vicinity of active arc systems, whereas the parental melt for dunites formed in subduction setting. The second part of this study measured trace element compositions for olivine, Cr-spinel and bulk rock of dunite. The measured bulk rock compositions are compared to those of calculated based on mineral chemistry and their abundance. This comparison suggests that the trapped melt fraction was negligible during the crystallization of the dunites. The calculated melt compositions for the dunites confirm that the melt formed in subduction setting.

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