Browsing by Subject "Chemical bonds"
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Item Analysis of factors affecting effective bond length of fiber reinforced polymer composite laminate externally bonded to concrete substrate(2012-05) Athawale, Parth; Bae, Sang-Wook; Morse, Stephen M.; Chen, XinzhongBond length is one of factors which are important with regards to the effective technique of improving the shear capacity of a concrete member by externally bonding fiber reinforcement polymer laminates. A number of models have been proposed by various researchers over the years but there is not a single model that can definitely predict the effective bond length (effective bond length). The models proposed show a disparity between the analytical and experimental values. This study takes a holistic approach to rationalize all the influencing factors. FEA is done of the existing experimental test results by calibrating for measured failure load and effective bond length values. A sensitivity study is undertaken to understand the influence of the affecting parameters on shear stress and effective bond length.Item Carbon-nitrogen double bond-forming elimination reactions involving 2-alkyl- and 2-arylpyrrolidines(Texas Tech University, 1980-05) Yilmaz, IbrahimNot availableItem Classical partial charge calculations(Texas Tech University, 1979-08) Hodge, Christopher AnthonyNot availableItem Development of hydrogen-mediated carbon-carbon bond formations(2005) Jang, Hye-Young; Krische, Michael J.Item Elimination reactions forming carbon-nitrogen double bonds(Texas Tech University, 1980-05) Cho, Bong-raeNot availableItem Energetics: the fundamental thermodynamic parameters of molecular complexation via electrostatic interactions in water(2003) Tobey, Suzanne Lai; Anslyn, Eric V.Item Hydrogen-mediated carbon-carbon bond formations: applied to reductive aldol and Mannich reactions(2007) Garner, Susan Amy, 1980-; Krische, Michael J.Hydrogen gas is the cleanest and most cost-effective reductant available to mankind, and the use of hydrogen gas in catalytic hydrogenation reactions is one of the oldest and most utilized organic reactions. Although catalytic hydrogenation has been practiced in industry on enormous scale, the use of hydrogen gas as a terminal reductant in C-C bond forming reactions has been limited to processes involving the migratory insertion of carbon monoxide such as: alkene hydroformylation and the Fischer-Tropsch reaction. A significant advance to the field of synthetic organic chemistry would be the expansion of C-C bond forming reactions beyond reductive coupling via carbon monoxide insertion. Herein, related metal catalyzed reductive couplings to [alpha],[beta]-unsaturated compounds in the presence of reducing agents such as: silane, borane, and hydrogen are reviewed. The following chapters discuss the development of hydrogen-mediated reductive aldol and Mannich reactions. The results from this body of work clearly demonstrate that hydrogen-mediated C-C bond forming reactions are emerging as a powerful tool for synthetic chemists.Item Novel calixpyrrole-like anion receptors(2004) An, Deqiang; Sessler, Jonathan L.Calix[n]pyrroles (n ≥ 4) are venerable anion receptors that are based on single pyrroles and ketones as building blocks. However, the existence of only one variable, n, that defines the nature of the systems, limits this class of macrocycles to only a few core structures. To overcome this limitation, a series of building blocks other than single pyrroles, have been applied to the construction of novel calixpyrrole-like systems. These building blocks include bipyrrole, furan, thiophene, and 1,3-bispyrrolylbenzenes. Based on bipyrrole as the sole building block, a series of calix[n]bipyrroles (n = 3, 4) was synthesized. Based on bipyrrole, furan or thiophene as co-building blocks, calix[2]bipyrrole[m]furan[n]thiophene (m + n = 2) were obtained. Based on 1,3- bispyrrolylbenzenes, calix[n]bispyrrolylbenzenes (n = 2 - 4) were synthesized. These novel calixpyrrole-like macrocycles contain different core structures than calix[n]pyrroles, and thus display different anion binding properties than their parent systems. This, in turn, means that these new systems are not only helping to the chemistry of calixpyrroles, but also giving rise to selective receptors that find applications in anion coordination chemistry.Item Orientation in vinyl activated 1,2-elimination reactions(Texas Tech University, 1979-05) Haines, Jeffrey CharlesNot availableItem Perturbations of the homo level of oxo-bridged chromium(III) dimers(Texas Tech University, 1992-12) Tekut, Thomas FrancisNot availableItem Rh-catalyzed reductive coupling under hydrogenation conditions and nucleophilic catalysis via phosphine conjugate addition(2007) Kong, Jongrock, 1972-; Krische, Michael J.At the threshold of the 21st centry, a new set of challenges is defined by the need to develop sustainable means of preparing chemical commodities demanded by society. Hence, such concepts as atom economy, step economy, and 'green chemistry' have become the requirements for the development of synthetic reactions. Hydrogenation is one of the most powerful catalytic methods which successfully satisfy the stated requirements of modern chemistry. Accordingly, catalytic hydrogenation has been tremendously utilized in industrial settings. The profound impact of hydrogenation portended a powerful approach to reductive carbon-carbon bond formation under hydrogenation conditions, resulting in the discovery of the Fischer-Tropsch process and hydroformylation. However, since this discovery, processes have restricted to the incorporation of a single carbon monoxide unit. Even though there are a few seminal contributions, systematic efforts toward the development of hydrogen-mediated carboncarbon bond forming processes beyond hydroformylation have been absent from the literature. In an exciting advance, the Krische group has shown that it is possible to reductively couple two or more organic molecules simply through their exposure to gaseous hydrogen in the presence of a metal catalyst. This finding has led to the development of a broad, new family of hydrogen-mediated C-C bond formation. Herein, related to hydrogen-mediated C-C bond formation, the overview of metal catalyzed intermolecular reductive coupling in the presence of reducing agents such as borane, silane, alane, metal, and hydrogen is presented. Chapter 2 describes systematic approaches to the development of hydrogen-mediated C-C bond formation and successful preliminary results achieved by our research group. Chapters 3 and 4 will describe the further extension of these hydrogen-mediated C-C bond formations including (1) hydrogen-mediated reductive couplings of conjugated alkynes with iminoacetates, (2) hydrogen-mediated reductive couplings of 1,3-enynes with [alpha]-ketoesters, and (3) hydrogen-mediated multicomponent reductive couplings. The development of catalytic systems for the nucleophilic activation of enones using phosphine catalysts has received attractive attention. Recently, an intramolecular variant of the Rauhut-Currier reaction was developed in our lab. To further extend nucleophilic phosphine catalysis, we have sought to develop new catalytic methodology via phosphine conjugate addition. Chapter 5 describes two new methodologies related to their area: (1) catalytic cycloallylation via nucleophilic phosphine catalysis and (2) allylic amination of Morita-Baylis-Hillman acetates.Item Sigma bond activation of the hydrogen molecule by cooperative interaction with a boron cation, a lithium anion, and a beryllium atom(Texas Tech University, 1999-05) Sharp, Stephanie BaxterSigma bond activation, making a sigma bond more reactive, has been one of tht' most extensively studied areas of chemistry for the past decade. Sigma bonds are the strongest bonds and therefore reactions that involve the breaking of such bonds have large activation energies. Without a doubt, the three most popular sigma bonds are H-H. C-H, and C-C which have been studied extensively in the chemical and physical sciences, and are the driving force behind many industrial processes. Activation of a sigma bond requires a reduction in the energy necessary to break the bond, and historically this has involved an interaction with a transition metal. The selective activation of alkanes has been identified as one of the Holy Grails of current chemical investigation [1].Item Studies of anion binding in pyrrole-containing supramolecular motifs(2002) Zimmerman, Rebecca Suzanne; Sessler, Jonathan L.Anions are important in a wide range of biological as well as chemical processes. In addition to their importance in the areas of medicine and catalysis, many environmental pollutants are anionic, such as phosphates, nitrates, and pertechnetate. Anions are more difficult to sense via electrostatic interactions than cations because of their lower charge to radius ratio; the majority of neutral anion receptors thus utilize hydrogen bonding as the predominant binding mode. Anions also have a wide range of geometries and require a high degree of complementarity in receptor design in order to achieve selectivity. Additionally, an anion receptor must successfully compete with the solvent environment. Anions are very strongly solvated, and the free energy gained upon binding must exceed the free energy lost as the result of dehydrating the anion. This can make binding in protic or hydroxylic solvents particularly challenging. Because of the inherent difficulties associated with anion recognition, the development of anion binding agents has lagged behind corresponding work on cation receptors. Currently, there are two general classes of synthetic anion receptors, those that are positively charged and those that are neutral. The major advantage of neutral hosts is that the absence of a positive charge generally provides for more selective binding, for the simple reason that positive charges are nondirectional and lead to electrostatic attractions that cannot by definition be selective for a particular anion. Another advantage to neutral hosts is that there is no inherent competition with a receptor associated with a counterion, which can often result in a weaker affinity for the intended guest. This dissertation focuses on the anion binding behavior of neutral, pyrrole containing supramolecular systems. The first chapter will discuss the ability of ferrocene-pyrrole conjugates to sense anions electrochemically. Chapter 2 investigates the anion binding ability of an expanded calixphyrin and a strapped calixpyrrole. Chapter 3 focuses on crown ether appended dipyrrolylquinoxalines and their effectiveness as ditopic receptors. Chapter 4 provides experimental methods and characterization data.Item Synthesis and characterization of an organocyclotriarsinetrioxide(Texas Tech University, 1979-05) McKerley, Billy JackNOT AVAILABLEItem The synthesis and study of group 13 element-transition metal complexes(Texas Tech University, 1996-12) Johnston, Thomas RichardReactions of indium(I) chloride with low-valent transition metal carbonyl compounds were shown to have only limited utility for producing indium-transition metal bonds. However, the reaction of indium(I) chloride with triruthenium dodecacarbonyl resulted in the synthesis and structural characterization of a new ruthenium carbonyl complex, Ru2(µ-Cl)2(µ-CO)(THF)2(CO)4 (THF = tetrahydrofuran), which contains coordinated tetrah>drofuran. The information gathered from these reactions indicated that indium-transition metal bonds might be formed if indium(I) chloride reacted with low-valent transition metal carbonyls that contain loosely coordinated solvent ligands. These reactions lead to the preparation of two new indiumtransition metal complexes, [(CH3)3NCH2Cl]3[Ru3(µ-InCl3)(µ-InCl2)(µ-CO)(CO)9l(CH3CN)(CH2Cl2)(l)and [(CH3)3NCH2Cl]2[Os(lnCl3)2(CO)4] (2). The crystal structure of 1 showed that the complex contains both the shortest and longest ruthenium-indium bonds yet reported, at 2.592(2) (A) and 2.793(1) (A), respectively. Another interesting feature of this compound is the coordination of InCl3 to two ruthenium atoms. Compound 2 contains the first reported bond between osmium and a Group 13 element other than boron. A reaction of Na2Fe(CO)4 with GaCl3 produced a new iron-gallium compound, Fe[GaCl2(THF)]2(CO)4, which was characterized by X-ray crystallography. The mechanism for this reaction was studied in order to gain a better understanding of the intermediates that are formed. These studies led to the supposition that a solventstabilized Fe(CO)4 fragment is an intermediate species in the reaction. A new method to produce activated indium metal via the disproportionation of indium(I) chloride in tetrahydrofuran was developed. The activated indium metal then reacted with Fe3(CO)i2 to give [Fe(CH3CN)6]2[Fe7ln2(CO)4o](CH3CN)2. The structure of this complex was determined by X-ray crystallography.Item Transition metal-catalyzed reductive C-C bond formation under hydrogenation and transfer hydrogenation conditions(2008-12) Ngai, Ming-yu, 1981-; Krische, Michael J.Carbon-carbon bond forming reactions are vital to the synthesis of natural products and pharmaceuticals. In 2003, the 200 best selling prescription drugs reported in Med Ad News are all organic compounds. Synthesizing these compounds involves many carbon-carbon bond forming processes, which are not trivial and typically generate large amounts of waste byproducts. Thus, development of an atom economical and environmentally benign carbon-carbon bond forming methodology is highly desirable. Hydrogenation is one of the most powerful catalytic reactions and has been utilized extensively in industry. Although carbon-carbon bond forming reactions under hydrogenation conditions, such as, alkene hydroformylation and the Fischer-Tropsch reaction are known, they are limited to the coupling of unsaturated hydrocarbons to carbon monoxide. Recently, a breakthrough was made by the Krische group, who demonstrated that catalytic hydrogenative C-C bond forming reactions can be extended to the coupling partners other than carbon monoxide. This discovery has led to the development of a new class of carbon-carbon bond forming reactions. Herein, an overview of transition metal-catalyzed reductive couplings of [pi]-unsaturated systems employing various external reductants is summarized in Chapter 1. Chapters 2-4 describe a series of rhodium- and iridium-catalyzed asymmetric hydrogenative couplings of various alkynes to a wide range of imines and carbonyl compounds. These byproduct-free transformations provide a variety of optically enriched allylic amines and allylic alcohols, which are found in numerous natural products, and are used as versatile precursors for the synthesis of many biologically active compounds. Transfer hydrogenation represents another important class of reactions in organic chemistry. This process employs hydrogen sources other than gaseous dihydrogen, such as isopropanol. The Krische group succeeded in developing a new family of transfer hydrogenative carbon-carbon bond formation reactions. Chapter 5 presents two novel ruthenium- and iridium-catalyzed transfer hydrogenative carbonyl allylation reactions. The catalytic system employing iridium complexes enables highly enantioselective carbonyl allylation from both the alcohol and aldehyde oxidation level. These systems define a departure from the use of preformed organometallic reagents in carbonyl additions that transcends the boundaries of oxidation level.