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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.
401

Dopage de la polyaniline et ses dérivés avec acides des Lewis - syntheses et proprietes spectroscopiques.

Bienkowski, Krzysztof 17 March 2006 (has links) (PDF)
Ce travail est consacré à l'étude du dopage de la polyaniline et de ses dérivés substitutés (polyanisidine, poly(2-ethylaniline)) avec d'une part le chlorure d'aluminium AlCl3 ou le chlorure ferrique FeCl3, d'autre part avec leurs dérivés contenant les ligands mixtes chlorure-acétylacétonate (AlCl2(acac) ou (FeCl(acac)2). Les polymères dopés avec AlCl3 ou FeCl3 sont conducteurs, et leur conductivité électronique est de l'ordre de 10-3 S/cm. Des études spectroscopiques complémentaires (UV-VIS-Proche IR, IRTF, RPE, RMN du noyau 27Al (dans le cas du dopage avec AlCl3) et spectroscopie Mössbauer sur le noyau 57Fe (dans le cas du dopage avec FeCl3)), combinées avec l'analyse élémentaire, permettent de comprendre et d'identifier un même mécanisme de dopage. Celui-ci correspond en un premier temps à une dissociation de la molécule du dopant. La partie cationique résultant de cette dissociation est complexée sur les sites azote de type imine de la chaîne du polymère, tandis que la partie anionique s'incorpore à la matrice polymère afin de neutraliser la charge positive imposée à la chaîne du polymère. La sphère de coordination du complexe cationique est complétée par solvatation avec une molécule de nitrométhane. Le réarrangement des charges accompagnant le processus de dopage entraîne la création de radicaux cationiques mobiles sur la chaîne du polymère, donnant ainsi au polymère dopé des propriétés de conduction électronique. Ce mécanisme rend parfaitement compte de la présence de porteurs de charge et de la structure cationique des radicaux de la chaîne polymérique dopée mises en évidence par les expériences de spectroscopie RPE et d'absorption UV-VIS-Proche IR. La polyaniline dopée avec FeCl3 présente de faibles propriétés mécaniques, qui peuvent cependant être améliorées par un traitement ultérieur avec l'hexafluoroacetylacetone (HFAA). Ce traitement conduit à la transformation de la polyaniline dopée avec FeCl3 (acide de Lewis) en un polymère dopé avec HFeCl4 (acide de Brönsted), simultanément plastifié par HFAA. Le dopage avec les ligands mixtes (AlCl2(acac) ou (FeCl(acac)2), bien qu'inopérant en ce qui concerne la polyaniline, conduit clairement au dopage de la polyanisidine et de la poly(2-éthylaniline). Les chaînes de ces polymères dopés présentent une structure radicalaire cationique mise en évidence par les expériences d'absorption UV-VIS-Proche IR ; mais le mécanisme de dopage reste plus complexe à définir que dans le cas du dopage avec AlCl3 ou FeCl3. Le dopage avec AlCl2(acac) conduit à un polymère dopé avec AlCl3 avec Al(acac)3 incorporé à la matrice du polymère comme sous-produit. Le dopage avec FeCl(acac)2 donne un composé présentant davantage de sites de fer non équivalents qu'il en est attendu ; leur nature reste difficile à identifier par spectrométrie Mössbauer.
402

Uncelebrated Stylists: Wyndham Lewis, Ford Madox Ford, and the Artist as Masochist

Erwin, Chase Morgan 01 August 2010 (has links)
This study presents an attempt to understand the political and aesthetic relationship between two of Modernism’s most enigmatic authors, Wyndham Lewis and Ford Madox Ford by examining their novelistic practice in light of their writings on politics and social criticism. A close look at the use of ironic distance, a hallmark feature in our understanding of modernist fiction, in Tarr (1918) and The Good Soldier (1915) reveals both authors conscious effort to distance themselves from their novel’s subjects, Fredric Tarr and John Dowell respectively. In light of both novels’ satirical element, a scathing attack on bourgeois narcissism caused by the wealthier class’ persistent attempts to identify with hollow and self serving social roles through the sham-aristocratic prestige created by England’s pre-war commodity culture, and the fact that both Fredric Tarr and John Dowell are artist figures that somehow resemble their creators, this project reinterprets Ford and Lewis’ ironic distance as an instance of self-distanciation. From this we can infer that both Ford and Lewis were invested in the modernist idea of impersonality, not just as a artistic or literary technique, but as the artist’s only means of escaping the narcissistic and slothful trap of modern subjectivity, and that, along with the production of modernist art, they saw a continual self-effacement as the price of authenticity, therefore inspiring in them the conviction to live as “uncelebrated stylists.”
403

Bispyridylamides as ligands in asymmetric catalysis

Belda de Lama, Oscar January 2004 (has links)
This thesis deals with the preparation and use of chiralbispyridylamides as ligands in metal-catalyzed asymmetricreactions. The compounds were prepared by amide formation usingdifferent coupling reagents. Bispyridylamides havingsubstituents in the 4- or 6- positions of the pyridine ringswere prepared by functional group interconversion of the 4- or6- halopyridine derivatives. These synthetic approaches provedto be useful for various types of chiral backbones. Pseudo C2-symmetric bispyridylamides were also synthesizedby means of stepwise amide formation. The compounds were used as ligands in themicrowave-accelerated Mocatalyzed asymmetric allylic alkylationreaction. Ligands having ð-donating substituents in the4-positions of the pyridine rings gave rise to products withhigher branched to linear ratio. The catalytic reaction, whichproved to be rather general for allylic carbonates with anaromatic substituent, was used as the key step in thepreparation of (R)-baclofen. The Mo-bispyridylamide catalystprecursor was studied by NMR spectroscopy. Bispyridylamide complexes of metal alkoxides were alsoevaluated in the asymmetric addition of cyanide to aldehydesand the metal complexes involved were studied by NMRspectroscopy and X-ray crystallography. Chiral diamines wereused as additives to study the ring opening of cyclohexeneoxide with azide, catalyzed by Zr(IV)-bispyridylamidecomplexes. Various bispyridylamides were attached to solid supports oforganic or inorganic nature. The solid-supported ligands wereused in Mo-catalyzed asymmetric allylic alkylation reactionsand in the asymmetric addition of cyanide to benzaldehyde. Keywords:asymmetric catalysis, chiral ligand, pyridine,amide, allylic alkylation, enantioselective, cyanation,ring-opening, chiral Lewis acid.
404

Synthesis, Characterization and Anion Binding Properties of Boron-based Lewis Acids

Zhao, Hai Yan 2012 May 1900 (has links)
The recognition and capture of fluoride, cyanide and azide anions is attracting great deal of attention due to the negative effects of these anions on the environment and on human health. One of common methods used for the recognition and capture of these anions is based on triarylboranes, the Lewis acidity of which can be enhanced via variation the steric and electronic properties of the boron substituents. This dissertation is dedicated to the synthesis of novel boron-based anion receptors that, for the most part, feature an onium group bound to one of the aryl substituents. The presence of this group is shown to increase the anion affinity of the boron center via Coulombic effects. Another interesting effect is observed when the onium group is juxtaposed with the boron atom. This is for example the case of naphthalene-based compounds bearing a dimesitylboryl moiety at one of the peri-position and a sulfonium or telluronium unit at the other peri position. Fluoride anion complexation studies with these sulfonium or telluronium boranes, show that the boron-bound fluoride anion is further stabilized by formation of a B-F->Te/S bridge involving a lp(F)->sigma*(Te/S-C) donor acceptor interaction. Some of the sulfonium boranes investigated have been shown to efficiently capture fluoride anions from wet methanolic solutions. The resulting fluoride/sulfonium borane adducts can be triggered to release a "naked" fluoride equivalent in organic solution and thus show promise as new reagents for nucleophilic fluorination chemistry. Interestingly, the telluronium systems show a greater fluoride anion affinity than their sulfonium analogs. This increase is assigned to the greater spatial and energetic accessibility of the sigma* orbital on the tellurium atom which favors the formation of a strong B-F->Te interaction. This dissertation is concluded by an investigation of the Lewis acidic properties of B(C6Cl5)3. This borane, which has been reported to be non-Lewis acidic by other researchers, is found by us to bind fluoride, azide and cyanide anions in dichloromethane with large binding constants. This borane is also reactive toward neutral Lewis bases, such as p-dimethylaminopyridine, in organic solvents.
405

Natural products from nonracemie building blocks : synthesis of pine sawfly pheromones

Larsson, Michael January 2005 (has links)
This thesis describes a number of synthetic approaches for obtaining chiral, enantiomerically pure natural products, in particular some semiochemicals. This has been accomplished by using various strategies; by starting from compounds from the chiral pool, by using chiral auxiliaries, via enzymatic resolutions or by chemical asymmetric synthesis. Hence, the sexual pheromone of Microdiprion pallipes, a propanoate ester of one or several isomers of 3,7,11-trimethyltridecan-2-ol, was synthesised, both as a mixture of all isomers and as the sixteen pure, individual stereoisomers. These compounds were obtained by joining different enantiopure building blocks stemming from the chiral pool. When compared with some synthetic blends, both the propanoate esters of the stereoisomeric erythro-3,7,11-trimethyltridecan-2-ols originally found in the extract from the female of M. pallipes, surprisingly, showed lower activities in biological studies. Indeed, the propanoates of two threo-isomers gave significantly higher responses in biological tests, than did the propanoates of the two natural erythro-ones. Because the synthetic strategy used earlier was not very efficient for the preparation of the threo-isomers of 3,7,11-trimethyltridecan-2-ol, we were encouraged to look for alternative synthetic approaches. The new synthetic strategy chosen led us to two key synthetic building blocks, an O-protected derivative of (2S,3S)-3-methyl-4-(phenylsulfonyl)butan-2-ol butanol and (3R,7R)-1-iodo-3,7-dimethylnonane. Deprotonation of the former followed by alkylation with the latter should give a compound with the desired carbon skeleton. For efficient preparation of the first building block, we developed a new diastereoselective addition reaction of dialkylzincs to some chiral aldehydes, the products of which were diastereomerically enriched 1,2-dialkyl-alkanols. Using this method, each enantiomer of the desired building block was obtained via efficient diastereoselective addition of dimethylzinc to each enantiomer of a 2-methylaldehyde. The resulting product, a diastereomerically and enantiomerically highly enriched 3-methyl-2-alkanol was further purified by enzyme catalysed acylation followed by some functional group interconversions. The second building block was prepared via convergent multistep synthesis, starting from a single, enantiomerically pure compound, (R)-2-methylsuccinic acid 4-t-butyl ester, derived from the chiral pool. The two enantiomerically pure building blocks, so obtained, were coupled together. Some additional functional group manipulations of the product produced furnished the desired isomer, which had shown the highest activity in field tests of the M. pallipes, namely the propanoate ester of (2S,3R,7R,11R)-3,7,11-trimethyltridecan-2-ol. This thesis describes a number of synthetic approaches for obtaining chiral, enantiomerically pure natural products, in particular some semiochemicals. This has been accomplished by using various strategies; by starting from compounds from the chiral pool, by using chiral auxiliaries, via enzymatic resolutions or by chemical asymmetric synthesis. Hence, the sexual pheromone of Microdiprion pallipes, a propanoate ester of one or several isomers of 3,7,11-trimethyltridecan-2-ol, was synthesised, both as a mixture of all isomers and as the sixteen pure, individual stereoisomers. These compounds were obtained by joining different enantiopure building blocks stemming from the chiral pool. When compared with some synthetic blends, both the propanoate esters of the stereoisomeric erythro-3,7,11-trimethyltridecan-2-ols originally found in the extract from the female of M. pallipes, surprisingly, showed lower activities in biological studies. Indeed, the propanoates of two threo-isomers gave significantly higher responses in biological tests, than did the propanoates of the two natural erythro-ones. Because the synthetic strategy used earlier was not very efficient for the preparation of the threo-isomers of 3,7,11-trimethyltridecan-2-ol, we were encouraged to look for alternative synthetic approaches. The new synthetic strategy chosen led us to two key synthetic building blocks, an O-protected derivative of (2S,3S)-3-methyl-4-(phenylsulfonyl)butan-2-ol butanol and (3R,7R)-1-iodo-3,7-dimethylnonane. Deprotonation of the former followed by alkylation with the latter should give a compound with the desired carbon skeleton. For efficient preparation of the first building block, we developed a new diastereoselective addition reaction of dialkylzincs to some chiral aldehydes, the products of which were diastereomerically enriched 1,2-dialkyl-alkanols. Using this method, each enantiomer of the desired building block was obtained via efficient diastereoselective addition of dimethylzinc to each enantiomer of a 2-methylaldehyde. The resulting product, a diastereomerically and enantiomerically highly enriched 3-methyl-2-alkanol was further purified by enzyme catalysed acylation followed by some functional group interconversions. The second building block was prepared via convergent multistep synthesis, starting from a single, enantiomerically pure compound, (R)-2-methylsuccinic acid 4-t-butyl ester, derived from the chiral pool. The two enantiomerically pure building blocks, so obtained, were coupled together. Some additional functional group manipulations of the product produced furnished the desired isomer, which had shown the highest activity in field tests of the M. pallipes, namely the propanoate ester of (2S,3R,7R,11R)-3,7,11-trimethyltridecan-2-ol. This thesis describes a number of synthetic approaches for obtaining chiral, enantiomerically pure natural products, in particular some semiochemicals. This has been accomplished by using various strategies; by starting from compounds from the chiral pool, by using chiral auxiliaries, via enzymatic resolutions or by chemical asymmetric synthesis. Hence, the sexual pheromone of Microdiprion pallipes, a propanoate ester of one or several isomers of 3,7,11-trimethyltridecan-2-ol, was synthesised, both as a mixture of all isomers and as the sixteen pure, individual stereoisomers. These compounds were obtained by joining different enantiopure building blocks stemming from the chiral pool. When compared with some synthetic blends, both the propanoate esters of the stereoisomeric erythro-3,7,11-trimethyltridecan-2-ols originally found in the extract from the female of M. pallipes, surprisingly, showed lower activities in biological studies. Indeed, the propanoates of two threo-isomers gave significantly higher responses in biological tests, than did the propanoates of the two natural erythro-ones. Because the synthetic strategy used earlier was not very efficient for the preparation of the threo-isomers of 3,7,11-trimethyltridecan-2-ol, we were encouraged to look for alternative synthetic approaches. The new synthetic strategy chosen led us to two key synthetic building blocks, an O-protected derivative of (2S,3S)-3-methyl-4-(phenylsulfonyl)butan-2-ol butanol and (3R,7R)-1-iodo-3,7-dimethylnonane. Deprotonation of the former followed by alkylation with the latter should give a compound with the desired carbon skeleton. For efficient preparation of the first building block, we developed a new diastereoselective addition reaction of dialkylzincs to some chiral aldehydes, the products of which were diastereomerically enriched 1,2-dialkyl-alkanols. Using this method, each enantiomer of the desired building block was obtained via efficient diastereoselective addition of dimethylzinc to each enantiomer of a 2-methylaldehyde. The resulting product, a diastereomerically and enantiomerically highly enriched 3-methyl-2-alkanol was further purified by enzyme catalysed acylation followed by some functional group interconversions. The second building block was prepared via convergent multistep synthesis, starting from a single, enantiomerically pure compound, (R)-2-methylsuccinic acid 4-t-butyl ester, derived from the chiral pool. The two enantiomerically pure building blocks, so obtained, were coupled together. Some additional functional group manipulations of the product produced furnished the desired isomer, which had shown the highest activity in field tests of the M. pallipes, namely the propanoate ester of (2S,3R,7R,11R)-3,7,11-trimethyltridecan-2-ol. / QC 20101026
406

Bifunctional Systems in the Chemistry of Frustrated Lewis Pairs

Zhao, Xiaoxi 08 January 2013 (has links)
Three classes of bifunctional compounds related to frustrated Lewis pair chemistry were studied. The first class, alkynyl-linked phosphonium borates, was strategically synthesized and the corresponding neutral alkynyl-linked phosphine boranes generated in solution. They were reacted with THF, alkenes and alkynes to undergo either ring-opening or multiple bond addition reactions, giving rise to zwitterionic macrocycles. In two select alkynyl-linked phosphonium borates, thermolysis resulted in unique rearrangements transforming the phosphino- and boryl-substituted alkynyl moieties into C4 chains. The alkynyl-linked phosphine boranes were further demonstrated to coordinate as η3-BCC ligands in Ni(0) complexes. The rigid nature of the coordination was confirmed by dimerization without cleavage of the Ni–B interaction upon the addition of acetonitrile or carbon monoxide. Moreover, reactions with Al-, Zn- and B-based Lewis acids prompted hydride transfer within the alkynyl-linked phosphonium borate and interesting functional group transfer reactions. The second class of the bifunctional systems, a series of gem-substituted bis-boranes, was subjected to reactions with tBu3P and CO2. The O-linked bis-borane was shown to coordinate the phosphino-carboxylate moiety with one B, while the methylene-linked bis-boranes were demonstrated to chelate the carboxyl group. The third bifunctional system class, vinyl-group tethered boranes, was examined to elucidate the mechanism of the frustrated Lewis pair addition reaction to olefins. Using a bis(pentafluorophenyl)alkylborane, the close proximity of the olefinic protons and the ortho-fluorine nuclei were evident by both NOE measurements and DFT calculations. Moreover, its reactions with phosphine bases suggested that an initial interaction between the highly electrophilic borane and the olefinic fragment precedes such frustrated Lewis pair addition reaction. Furthermore, a bis(pentafluorophenyl)alkoxyborane was synthesized and reacted with P-, N-, C- and H-based nucleophiles, demonstrating the wide range of Lewis bases that can be applied in olefin addition reactions with complementary regioselectivity.
407

Exploring New Synthetic Routes to Frustrated Lewis Pairs

Tanur, Cheryl 25 August 2011 (has links)
Gold(I) and copper(I) imidazolium complexes were synthesized and probed for use as bulky Lewis acids in frustrated Lewis pairs (FLPs) with bulky phosphines and amines. Their reactivity with small molecules was investigated and the compounds were fully characterized by multinuclear NMR spectroscopy, elemental analysis and X-ray crystallography. Secondly, a new methylene-linked boron-sulfur Lewis acid was synthesized. Its thermodynamic properties were determined and its reactivity with terminal and internal alkynes was demonstrated. Adducts and heterocycles of this boron-sulfur system were fully characterized by multinuclear NMR spectroscopy, elemental analysis and X-ray crystallography. The application of these new systems for the activation of small molecules is described in this thesis.
408

Exploring New Synthetic Routes to Frustrated Lewis Pairs

Tanur, Cheryl 25 August 2011 (has links)
Gold(I) and copper(I) imidazolium complexes were synthesized and probed for use as bulky Lewis acids in frustrated Lewis pairs (FLPs) with bulky phosphines and amines. Their reactivity with small molecules was investigated and the compounds were fully characterized by multinuclear NMR spectroscopy, elemental analysis and X-ray crystallography. Secondly, a new methylene-linked boron-sulfur Lewis acid was synthesized. Its thermodynamic properties were determined and its reactivity with terminal and internal alkynes was demonstrated. Adducts and heterocycles of this boron-sulfur system were fully characterized by multinuclear NMR spectroscopy, elemental analysis and X-ray crystallography. The application of these new systems for the activation of small molecules is described in this thesis.
409

Silicon Tetrachloride Mediated Asymmetric Aldol Addition Reaction

Tan, Duygu 01 January 2013 (has links) (PDF)
Aldol addition reaction is one of the most important and most studied carbon-carbon bond forming reactions in organic chemistry. Recent studies focused on the catalytic version of this chemistry. Different from the classical Mukaiyama-type aldol reactions, chiral lewis bases have been used as promoters. In the presence of SiCl4, these reactions proceed through a cyclic transition state leading to anti aldol product as a major product with moderate-to-good diastereo and enantioselectivities. Phosphoramide derivatives, BINAPO, BINAPO derivatives, N,N-dioxides and N-oxides have been extensively used for this purpose. Recently, our group has designed new phosphine oxy aziridinyl phosphonates (POAP) as chiral Lewis bases. These promoters were used for the asymmetric aldol addition reaction between cyclohexanone and different aldehydes in the presence of SiCl4. Moreover, our previously designed phosphine oxy ferrocenyl substituted aziridinyl methanol (POFAM) ligands were also tested as Lewis bases. Among these 6 potential promoters, POAP-A gave the best results, and the aldol product were obtained in moderate to good yields up to 80%, and with moderate enantioselectivities (the highest, 66%) after standard optimization studies. Aldehyde screening experiments provided the highest enantioselectivity (68%) with 2- naphthaldehyde.
410

Certain variables related to the change in cultural interests of Lewis and Clark College freshmen

Ennis, George William 16 April 1956 (has links)
Graduation date: 1956

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