• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 381
  • 64
  • 63
  • 40
  • 27
  • 22
  • 16
  • 14
  • 12
  • 12
  • 12
  • 12
  • 12
  • 12
  • 11
  • Tagged with
  • 797
  • 125
  • 109
  • 108
  • 99
  • 83
  • 73
  • 58
  • 55
  • 55
  • 44
  • 44
  • 42
  • 39
  • 38
  • 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.
51

Some uses of acyliminium ions in the synthesis of isoquinolones with potential biological activity

Taha, Mutasem O. January 1998 (has links)
The preparation of a number of 2-substituted homophthalimides through the condensation of homophthalic anhydride with different arylalkyl arnines is reported. The prepared compounds were alkylated at the 4-position to generate 4-mono-, 4,4-disubstituted and 4-spirocyclic homphthalimides, the analogues of which were reported to have interesting biological activity. Regioselective reduction of the 4-substituted derivatives generated the corresponding carbinolamides. Treating the carbinolamides with mineral or Lewis acids generated N-acyliminiurn ions, which were trapped in situ by one of the following: ( 1) aromatic neucleophiles to generate analogues of the natural product berberine, (2) alkyl chain migration to generate tetrahydrophenanthridones and functionalised isoquinolones, (3) cyclopropane ring-opening to generate 4-alkylisoquinolones, (4) addition to double bond to generate cyclopentaisoquinolones and (5) benzyl or allyl elimination. The oxidation of 4-monosubstituted homophthalimides with triplet dioxygen in alkaline media was investigated, and it generated 4-hydroxyhomophthalimides and isobenzofurancarboxamides. Treating isobenzofurancarboxamides with POCI3 provided a concise route to analogues of the neuroactive naturally-occurring phthalideisoquinolines.
52

Herbert Lewis and Welsh radicalism : A study of the political career of John Herbert Lewis (1858-1933) with special reference to the period 1892-1906

Erasmus, T. P. January 1988 (has links)
No description available.
53

Gas-phase reactivity of Lewis adducts and model biochemical systems : quantum chemistry and molecular dynamics perspectives / Réactivité à la phase gazeuse de Lewis adduit et de systèmes biochimiques modèle : chimie quantique et dynamique moléculaire perspectives

Martín Sómer, Ana 17 October 2014 (has links)
La réactivité à la phase gazeuse, ou réactivité intrinsèque, a une grande importance puisque l’absence d’interactions avec un solvant peut donner lieu à une réactivité très diffèrent donc, nous permettant d’avoir une meilleure connaissance des propriétés moléculaires. Avec l’émergence en 1900 de nouvelles techniques expérimentales, plus précisément des techniques pour ioniser plus doucement, la chimie des ions en phase gazeuse s’est développée significativement et a supposé en changement dans l’idée de la réactivité chimique. Cet manuscrit est divisé en deux parties chacune d’elles concernant un aspect diffèrent de la réactivité en phase gazeuse.La premier partie, Part I, étude l’acidité intrinsèque d’une série de bases de Lewis du groupe 15 du tableau périodique, l’accent étant mis sur le changements d’acidité ayant lieue après la formation du complexe de Lewis. Divers acides de Lewis appartenant ou groupe 13 on été tenus en compte. Afin d’expliquer l’origine de l’augment d’acidité observé plusieurs méthodes théoriques on été employés. Pour le calcul de l’acidité intrinsèque ont a employé la théorie de la fonctionnelle de la densité (DFT, sigle pour Density Functional Theory) et des méthodes qui sont basées à la fonction d’onde. Pour décrire les variations dans la configuration électronique ayant lieu à la formation du complexe (et qui sont les responsables du changement d’acidité susmentionné) nous avons utilisé des méthodes complémentaires pour l’analyse de la population électronique (AIM, ELF et NBO). Il est important de souligner qu’une partie des résultats présentés dans cet manuscrit on été déjà corroborés par les résultats expérimentaux.La deuxième partie, Part II, est centrée sur l’étude de la réactivité unimoléculaire des ions formamide-M2+ (M = Ca, Sr). Dans ce cas particulier, les ions choisis avaient été déjà étudiés expérimentalement avec la technique de dissociation induite par collision (CID, sigle pour Collision Induced Dissociation). Tout au long de cette deuxième partie, nous avons étudié et caractérisé les différents mécanismes de fragmentation des deux ions, en utilisant diffèrent méthodes théoriques qui sont complémentaires entre eux. Premièrement, ont a évalué divers fonctionnelles afin de trouver le plus approprié pour maintenir le coût computationnelle bas au même temps que d’obtenir des résultats fiables. Ensuite, on a modélisé par moyen de simulations de dynamique la réactivité aux temps courts (< 2.5 femto seconds). En outre, en se servant des données obtenues antérieurement, on a étudié la cinétique de fragmentation avec la théorie statistique RRKM, pour les réactions «lents » (t > 2.5 fs). L’utilisation de cette procédure multi-échelle nous permet de rationaliser l’origine de tous les produits observés expérimentalement ainsi que de donner une explication aux différences entre les deux ions considérés. Pour finir, dans le quatrième chapitre sont énumérés et décrits brièvement les différents méthodes employés au cours de cet travail, tant théorétiques que expérimentaux. / The so-called intrinsic reactivity (gas-phase reactivity) is of great importance since the absence of interaction with a solvent can result in very different reactivity patterns, allowing for a better understanding of molecular properties. With the advent in the 1900s of new experimental techniques, notably soft ionization methods such as electrospray ionization, the gas-phase ion chemistry has significantly developed in the last decades of the 1900s with a concomitant change in our view of chemical reactivity. The present manuscript is divided in two different parts, each one dealing with different aspects of gas-phase reactivity.Part I is concerned with the study of the intrinsic acidity of a series of group 15 Lewis bases. The changes on the aforementioned intrinsic acidity as the Lewis bases form adducts with group 13 Lewis acids is the main subject of this part. Thus, the origin for the acidity enhancement observed upon adduct formation is rationalized by means of different theoretical methods. High-level DFT and ab initio calculation were performed in order to compute theoretical acidities of the molecules under survey. Complementary to this, population analysis techniques such as AIM, ELF, and NBO were used to analyze the changes on the electronic configurations of those molecules and therefore provide with an explanation to the observed acidities. It is worth to stress the fact that part of the results were as well confirmed by means of experimental measurements. Part II focuses in unimolecular reactivity of molecular ions, namely, formamide-M2+ (M = Ca, Sr). In this case, experiments studying the Collision Induced Reactivity (CID) of these ions were already performed and through the second part of this manuscript the fragmentation mechanism of both ions are studied and characterized using different, but complementary, theoretical techniques. It is worth to mention that in a very first-step, an assessment of different methods to perform reliable electronic structure calculations while maintaining the lower possible computational cost. In the one hand, a kinetic study of the fragmentation process using the statistical theory RRKM, to describe the long-time reactivity (> fs). On the other hand, direct dynamics simulations are performed in order to describe the short-time (< 2.5 fs) non-statistical reactivity. This multi-scale approach allowed us to account for all the products observed in the CID experimental spectra of formamide-M2+ ( M = Ca, Sr), as well as the differences between them. In the fourth chapter a summary of the experimental and theoretical procedures used to perform the work presented in this manuscript is provided.
54

The Portrayal of Evil in C.S. Lewis’s The Horse and His Boy

Wiklund, Johanna January 2006 (has links)
<p>Abstract</p><p>C.S. Lewis’s Chronicles of Narnia (there are seven books all together) are often perceived as children’s books that in a simple and uncomplicated way convey the positive message of Christianity. However, Lewis’s intention was as much to deal with negative moral issues such as selfishness, dishonesty, betrayal, cruelty, vindictiveness and hypocrisy, in other words: aspects of evil. The purpose of this essay is to examine C.S. Lewis’s portrayal of evil in the Chronicles of Narnia, in order to show the novel’s complexity. My main focus will be on one of the lesser known of the books, The Horse and His Boy.</p><p>I believe that Lewis through his books convey the complexity of live, but through a perspective which makes it easier for children to accept. All the ingredients of real life are included in the Chronicles, even the ugly side to life, namely evil. By displaying the phenomenon of evil in so many different ways in his books, I believe that Lewis is trying to show the complexity which lies in the workday world as well as in heaven and the world of fantasy. Lewis uses evil as an expression to encourage the moral imagination within the readers. I believe that he urges his readers to take a stand and see what evil is and what it does. Lewis demonstrates that good and evil is in each and every one of us, and that it is the choices we make that defines us.</p>
55

The Portrayal of Evil in C.S. Lewis’s The Horse and His Boy

Wiklund, Johanna January 2006 (has links)
Abstract C.S. Lewis’s Chronicles of Narnia (there are seven books all together) are often perceived as children’s books that in a simple and uncomplicated way convey the positive message of Christianity. However, Lewis’s intention was as much to deal with negative moral issues such as selfishness, dishonesty, betrayal, cruelty, vindictiveness and hypocrisy, in other words: aspects of evil. The purpose of this essay is to examine C.S. Lewis’s portrayal of evil in the Chronicles of Narnia, in order to show the novel’s complexity. My main focus will be on one of the lesser known of the books, The Horse and His Boy. I believe that Lewis through his books convey the complexity of live, but through a perspective which makes it easier for children to accept. All the ingredients of real life are included in the Chronicles, even the ugly side to life, namely evil. By displaying the phenomenon of evil in so many different ways in his books, I believe that Lewis is trying to show the complexity which lies in the workday world as well as in heaven and the world of fantasy. Lewis uses evil as an expression to encourage the moral imagination within the readers. I believe that he urges his readers to take a stand and see what evil is and what it does. Lewis demonstrates that good and evil is in each and every one of us, and that it is the choices we make that defines us.
56

The Viability of David Lewis's Theory of Humean Supervenience

Kerchner, Breanna January 2011 (has links)
<p>I present a defense of David Lewis's metaphysical theory of Humean Supervenience. I provide novel motivations for his theory, and look to current physical science research for support of the metaphysical theory. I draw heavily on analogies between Humean Supervenience and classical discussions of the nature of space-time. I also defend Humean Supervenience against four major philosophical objections using considerations from physics and metaphysics.</p> / Dissertation
57

Synthesis and material properties of supramolecules containing fluorinated organomercurials

Taylor, Thomas Jackson 15 May 2009 (has links)
This dissertation details the synthesis and analysis of novel supramolecular species that feature simple fluorinated organomercurials, such as trimeric perfluoroortho- phenylene mercury ([o-C6F4Hg]3). These organomercurials can complex a variety of unsaturated substrates including arenes and alkynes. The major emphasis was on developing molecular architectures that are held together in part by secondary Hg-Calkyne interactions. Diphenylpolyynes, hydrocarbons featuring extended regions of unsaturation, were found to complex with [o-C6F4Hg]3 in a series of adducts. While the internal structures of the hydrocarbons themselves were found to be basically unaltered, within the crystals the polyynes were physically separated from one another by intervening molecules of [o-C6F4Hg]3, preventing them from cross-linking. This leads to a substantial stabilizing effect, for example [o-C6F4Hg]3 and Ph(CC)4Ph form a 2:1 adduct that is stable at temperatures up to 120 ºC above the pure hydrocarbon. Adducts of [o-C6F4Hg]3 and molecules containing a 1,3,5-triethynyl benzene core display a variety of novel properties. 1,3,5-tris(trimethylsilylethynyl) benzene forms binary supramolecular stacks with [o-C6F4Hg]3. The structure also displays large cylindrical 1-dimensional cavities. These cavities are lined with non-polar groups, have an internal diameter of 6.2 Å, and remain stable in the absence of guests. The compound readily interacts with and reversibly adsorbs simple alkanes. 1,3,5-tris(phenylethynyl) benzene forms similar stacks with [o-C6F4Hg]3, albeit without the cavities. Upon irradiation with visible and ultraviolet light, this adduct emits a long-lived emission that was hitherto unreported. From computer calculations and lifetime measurements, it appears this radiation is the phosphorescence of the pure hydrocarbon. Intensive structural studies have also been performed on adducts containing polyaromatic compounds, including phenanthrene, and the organomercurials [o- C6F4Hg]3, pentafluorophenyl mercury chloride and bromide. These experiments were performed to determine if Lewis acid-p complexes could be made with monofunctional mercury compounds. Polyaromatic hydrocarbons, such as phenanthrene and diphenylacetylene, were used as the substrates for these investigations. While all the mercurials formed adducts with the substrates, the photophysical measurements were not uniform and indicate that [o-C6F4Hg]3 has a stronger heavy-atom effect because of the cooperativity of the three mercury atoms.
58

Trimeric perfluoro-ortho-phenylene mercury as a building block for supramolecular materials

Haneline, Mason Reames 12 April 2006 (has links)
Trimeric perfluoro-ortho-phenylene mercury (1) constitutes one of the simplest trifunctional Lewis acidic hosts. Cooperative effects arising from the proximity of the mercury(II) centers, the electron-withdrawing properties of the backbone and the accessibility of the electrophilic sites leads to the facile complexation of neutral and electron rich substrates. The planarity of the structure as well as its overall polarizability compounded with relativistic effects at mercury also permits the occurrence of non-covalent interactions. The main objective of this dissertation was to explore the potential of 1 as a building block for supramolecular materials. Compound 1 was investigated using single crystal x-ray diffraction and was found to display a rich polymorphism. The electronic structure, probed by DFT methods, shows that the LUMO of 1 has a large contribution from the mercury 6p orbitals and features a large lobe protruding above and below the center of the trinuclear mercury core. Complexes in which two nitronyl nitroxide radicals (NIT-Ph = 2-(phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) coordinate to the trinuclear core of 1 above and below the Hg3 plane reveal that 1 does not significantly mediate magnetic interactions. The ability of 1 to complex &#960;-basic molecules such as tetrathiafulvalene (TTF), toluene, o-xylene, m-xylene, p-xylene, mesitylene, biphenyl, naphthalene, acenaphthalene, anthracene, pyrene, triphenylene, perylene, and coronene was also investigated and show that 1 and arenes form extended binary stacks in which the two components alternate. The photoluminescence observed in some of these supramolecular complexes corresponds to the phosphorescence of the arene indicating a mercury heavy atom effect. Complexation of 1 in solution was observed with hexaalkoxytriphenylenes (HATn, n = 1, 6) by fluorescence and NMR spectroscopy. Finally, compound 1 forms electrophilic double sandwich structures with ferrocene and nickelocene in which a molecule of 1 caps each of the Cp ligands. The nickelocene adduct is stabilized towards oxidation, and the photophysical and magnetic properties indicate the occurrence of a mercury heavy atom effect.
59

The evolution of ideas : John Lewis Gaddis and the "remarkably durable" war /

Feeley, Meghan M., January 2009 (has links)
Thesis (M.A.) -- Central Connecticut State University, 2009. / Thesis advisor: Jay Bergman. "... in partial fulfillment of the requirements for the degree of Master of Arts in History." Includes bibliographical references (leaves 69). Also available via the World Wide Web.
60

Design and evaluation of a new Lewis acid-assisted Lewis acid catalyst system and further applications of a double-allylation reagent

Sivasubramaniam, Umakanthan Unknown Date
No description available.

Page generated in 0.0217 seconds