UNT Libraries - 37 Matching Results

Search Results

(4+2)-Cycloaddition Reactions of Ketenes; Pyranones

Description: This study deals with the (4+2)-cycloaddition reactions of 4-π electron compounds with ketenes. Chloroketenes were generated in situ from the corresponding chlorinated acid chlorides in the presence of the ketenophiles. Chloro-, dichloro- and diphenylketenes reacted with 1-methoxy-3-trimethylsiloxy-l,3-butadiene, and 2,4-bis(trimethylsiloxy)-1,3-pentadiene to yield the corresponding dihydropyrans. The dihydropyrans yielded substituted 4-pyranones on hydrolysis.
Date: August 1983
Creator: Agho, Michael O. (Michael Osarenogowu)

Computational studies of the potential energy surface for O(³P) + H₂S: Characterization of transition states and the enthalpy of formation of HSO and HOS

Description: Article on computational studies of the potential energy surface for O(³P) + H₂S and the characterization of transition states and the enthalpy of formation of HSO and HOS.
Date: January 1, 1995
Creator: Goumri, Abdellatif; Laakso, Dianna; Rocha, John-David Ray; Smith, C. E. & Marshall, Paul

Conformational Analysis Using Carbon-13-Carbon-13 and Carbon-13-Hydrogen Spin-Spin Coupling Constants

Description: This study consists of four major areas of research. First, the relationship between and was extended to Lrl nil homoallylic couplings and was used to determine the relative degree of puckering in a series of dihydroaromatic carboxylic acids. Second, the effect of coupling contributions transmitted through space were examined by theoretical calculations of the intermediate neglect of differential overlap finite perturbation theory type (INDO-FPT) including selective overlap reduction experiments to determine the sign and magnitude of the major through-space contributions and the effect of the orientation of the substituent upon the vicinal carbon3 carbon coupling. Third, the dependence of the J upon substituent orientation in norbornanes was empirically investigated by the synthesis of a series of lactones and cyclic ethers whose conformation was rigid and known. Fourth, a large number of norbornanes substituted with methyls in the 1, 3, and 7 position and a carbon-13 labeled substituent in the 2 position were synthesized and studied in order to obtain a variety of vicinal C-C couplings; all the NMR parameters for this series of compounds were determined while the carbon13 labeled substituent was varied from methyl to methylene to carbinol to aldehyde and to carboxylic acid.
Date: May 1981
Creator: McDaniel, Cato R., Jr.

GC/MS Analysis of Chlorinated Organic Compounds in Municipal Wastewater After Chlorination

Description: A study has been conducted for the qualitative and Quantitative analysis of chlorinated organic compounds in water. The study included the adaptation of Amberlite XAD macroreticular resin techniques for the concentration of municipal wastewater samples, followed by GC/MS analysis. A new analytical method was developed for the determination of volatile halogenated organics using liquid-liquid extraction and electron capture gas chromatography. And, a computer program was written which searches raw GC/MS computer files for halogen-containing organic compounds.
Date: August 1982
Creator: Henderson, James E. (James Edward)

The Influence of Selected Non-Bonded Interactions on Vicinal Carbon-Carbon Coupling Constants

Description: The body of information concerning carbon-carbon spin-spin coupling constants now includes a large number of coupling constants, the establishment of a dihedral angular dependence on 3JCC, and the application of 3JCC to conformational analysis. This study adds another dimension to the growing wealth of information associated with 13 C-NMR: the influence of some non-bonded interactions on 3JCC Four types of non-bonded interactions that could influence vicinal carbon-carbon NMR coupling constants were investigated. To facilitate the NMR studies, a variety of 13C-labeled compounds were synthesized.
Date: May 1982
Creator: Canada, Edward D. (Edward Dee)

The Mechanisms of Methane C–H Activation and Oxy-insertion Via Small Transition Metal Complexes: a DFT Computational Investigation

Description: Our country continues to demand clean renewable energy to meet the growing energy needs of our time. Thus, natural gas, which is 87% by volume of methane, has become a hot topic of discussion because it is a clean burning fuel. However, the transportation of methane is not easy because it is a gas at standard temperature and pressure. The usage of transition metals for the conversion of small organic species like methane into a liquid has been a longstanding practice in stoichiometric chemistry. Nonetheless, the current two-step process takes place at a high temperature and pressure for the conversion of methane and steam to methanol via CO + H2 (syngas). The direct oxidation of methane (CH4) into methanol (CH3OH) via homogeneous catalysis is of interest if the system can operate at standard pressure and a temperature less than 250 C. Methane is an inert gas due to the high C-H bond dissociation energy (BDE) of 105 kcal/mol. This dissertation discusses a series of computational investigations of oxy-insertion pathways to understand the essential chemistry behind the functionalization of methane via the use of homogeneous transition metal catalysis. The methane to methanol (MTM) catalytic cycle is made up of two key steps: (1) C-H activation by a metal-methoxy complex, (2) the insertion of oxygen into the metal−methyl bond (oxy-insertion). While, the first step (C-H activation) has been well studied, the second step has been less studied. Thus, this dissertation focuses on oxy-insertion via a two-step mechanism, oxygen-atom transfer (OAT) and methyl migration, utilizing transition metal complexes known to activate small organic species (e.g., PtII and PdII complexes). This research seeks to guide experimental investigations, and probe the role that metal charge and coordination number play.
Date: May 2014
Creator: Prince, Bruce M.

Molecular Dynamics and Interactions in Liquids

Description: Various modern spectroscopies have been utilized with considerable success in recent years to probe the dynamics of vibrational and reorientational relaxation of molecules in condensed phases. We have studied the temperature dependence of the polarized and depolarized Raman spectra of various modes in the following dihalomethanes: dibromomethane, dichloromethane, dichloromethane-d2, and bromochloromethane. Among other observed trends, we have found the following: Vibrational dephasing times calculated from the bend) and (C-Br stretch) lineshapes are of the same magnitude in CI^B^. The vibrational dephasing time of [C-D(H) stretch] is twice as long in CD2Cl2 as in CH-^C^, and the relaxation time of (C-Cl stretch) is greater in CI^C^ than in CD2CI2. Isotropic relaxation times for all three stretching vibrations are significantly shorter in C^BrCl than in CI^C^ or CI^B^. Application of the Kubo model revealed that derived modulation times are close to equal for equivalent vibrations in the various dihalomethanes. Thus, the more efficient relaxation of the A^ modes in CE^BrCl can be attributed almost entirely to the broader mean squared frequency perturbation of the vibrations in this molecule.
Date: May 1985
Creator: Chen, Jen Hui

The Multi-reference Correlation Consistent Composite Approach: A New Vista In Quantitative Prediction Of Thermochemical And Spectroscopic Properties

Description: The multi-reference correlation consistent composite approach (MR-ccCA) was designed to reproduce the accuracy of more computationally intensive ab initio quantum mechanical methods like MR-ACPF-DK/aug-cc-pCV?Z-DK, albeit at a significantly reduced cost. In this dissertation, the development and applications of the MR-ccCA method and a variant of its single reference equivalent (the relativistic pseudopotential ccCA method) are reported. MR-ccCA is shown to predict the energetic properties of reactive intermediates, excited states species and transition states to within chemical accuracy (i.e. ±1.0 kcal mol 1) of reliable experimental values. The accuracy and versatility of MR-ccCA are also demonstrated in the prediction of the thermochemical and spectroscopic properties (such as atomization energies, enthalpies of formation and adiabatic transition energies of spin-forbidden excited states) of a series of silicon-containing compounds. The thermodynamic and kinetic feasibilities of the oxidative addition of an archetypal arylglycerol ?-aryl ether (?-O-4 linkage) substructure of lignin to Ni, Cu, Pd and Pt transition metal atoms using the efficient relativistic pseudopotential correlation consistent composite approach within an ONIOM framework (rp-ccCA-ONIOM), a multi-level multi-layer QM/QM method formulated to enhance the quantitative predictions of the chemical properties of heavy element-containing systems larger than hitherto attainable, are also reported.
Date: December 2011
Creator: Oyedepo, Gbenga A.

A New Chromophoric Organic Molecule Toward Improved Molecular Optoelectronic Devices

Description: The characterization of 2,3,6,7,10,11-hexabromotriphenylene, Br6TP, is presented toward its potential use as an n-type organic semiconductor and metal-free room temperature phosphor. The crystal structure shows both anisotropic two-dimensional BrBr interactions and inter-layer ?-stacking interactions. Photophysical characteristics were evaluated using solid-state photoluminescence and diffuse reflectance spectroscopies, revealing significantly red-shifted excitations in the visible region for the yellow solid material (compared to ultraviolet absorption bands for the colorless dilute solutions). Correlation of spectral, electrochemical, and computational data suggest the presence of an n-type semiconducting behavior due to the electron-poor aromatic ring. The material shows excellent thermal stability as demonstrated by thermogravimetric analysis and infrared spectra of a thin film deposited by thermal evaporation. The potential for Br6TP and its analogues toward use in several types of photonic and electronic devices is discussed.
Date: December 2012
Creator: Halbert, Jason Paul

Ozonolysis and Cycloaddition Reaction of (Trimethylsilyl)ketene

Description: The purpose of this investigation was to study the chemistry of the new and novel (trimethylsilyl)ketene. This ketene was synthesized by pyrolysis of (trimethylsilyl)ethoxyacetylene which was prepared from ethoxyacetylene and methyllithium. (Trimethylsilyl)ketene is a very stable and isolable ketene which does not dimerize and, therefore, provides an opportunity for some unique studies that have not been possible with other monosubstituted ketene.
Date: August 1980
Creator: Saidi, Kazem

The Preparation, Properties, and Reactions of Silenes, Silenoids, and 2-Silanobornenes

Description: The reaction of chlorodimethylvinylsilane with tertbutyllithium was investigated in the presence of several conjugated dienes. In all cases except with 2,5-dimethylfuran, [2+4] cycloadducts of a silene intermediate are obtained in hydrocarbon solvents. The presence of THF in the reaction mixture suppresses the formation of cycloadducts in favor of 1,3-disilacyclobutanes. In the reaction of dimethylethoxyvinylsilane or dimethylmethoxyvinylsilane with tert-butyllithium the main product is the 1,1-dimethyl2-neopentyl-4-(dimethylalkoxysilyl)silacyclobutane. It is concluded that lithium chloride elimination to give silene intermediates occurs in hydrocarbon solvents. In the presence of strong Lewis bases or when the leaving group on silicon is an alkoxy group, the addition reaction giving a-lithiosilanes occurs and products arising from their coupling reactions are obtained.
Date: December 1981
Creator: Pierce, Richard A. (Richard Austin), 1918-2004