UNT Libraries - 83 Matching Results

Search Results

Results: 1 - 24 next
open access

Solution Studies of ⁶Li Enriched Organolithium Compounds Using New NMR Techniques

Description: With the values of 6Li T1 measured and the literature values of J(13C-6Li) for these compounds, three new 13C NMR techniques are developed for the analysis of organolithium compounds. Modifications to the spectrometer are discussed, as well as calibrations of the 6Li decoupler channel needed to set up these new experiments. The theoretical development of each technique is presented, as well as data from their verification, using organolithium compounds of known structure. Once qualified, the ne… more
Date: May 1990
Creator: Ellington, Donald H. (Donald Howard)
Item Type: Refine your search to only Thesis or Dissertation
open access

Syntheses and Structures of Substituted Polycyclic Molecules and Analysis of the Two-Dimensional NMR Spectrum of Thiele's Ester

Description: Diels-Alder cycloaddition of methylcyclopentadienes to 2,5-dibromo-p-benzoquinone was performed. A single, isomerically pure cycloadduct was isolated, whose structure was assigned via analysis of its 1-D and 2-D NMR spectra. Diels-Alder cycloaddition of methylcyclopentadienes to 2 -methoxy-p-benzoquinone was performed. A single, isomerically pure cycloadduct was isolated, whose structure was assigned via analysis of the 1-D and 2-D NMR spectra of this cycloadduct and its reduction product obtai… more
Date: May 1990
Creator: Lu, Shao-Po
Item Type: Refine your search to only Thesis or Dissertation
open access

Synthesis, Structure, and Solution Dynamics of Co₄(CO)₈(dmpe)(mu₄-PPh)₂

Description: Reaction of the tetracobalt cluster Co4(CO)10(t 4-PPh)2 with 1,2-bis(dimethylphosphino)ethane (dmpe) affords the bis-substituted cluster Co4(CO)8(dmpe)(t 4-PPh)2. The bidentate dmpe ligand is shown to bind to the cluster in a chelating fashion by IR, NMR, and X-ray diffractions analyses. The fluxional nature of the ancillary carbonyl groups has been studied by variable temperature 13C NMR measurements which reveal two distinct carbonyl scrambling pathways. The stability of the phosphine-ligated… more
Date: May 1990
Creator: Schulman, Cheryl Lutins
Item Type: Refine your search to only Thesis or Dissertation
open access

The Analysis of PCDD and PCDF Emissions from the Cofiring of Densified Refuse Derived Fuel and Coal

Description: The United States leads the world in per capita production of Municipal Solid Waste (MSW), generating approximately 200 million tons per year. By 2000 A.D. the US EPA predicts a 20% rise in these numbers. Currently the major strategies of MSW disposal are (i) landfill and (ii) incineration. The amount of landfill space in the US is on a rapid decline. There are -10,000 landfill sites in the country, of which only 65-70% are still in use. The Office of Technology Assessment (OTA) predicts an 80%… more
Date: August 1990
Creator: Moore, Paul, 1962-
Item Type: Refine your search to only Thesis or Dissertation
open access

Aqueous Solubilities and Transformation of Chlorinated Benzenes

Description: Aqueous solubilities of twelve chlorinated benzenes were determined by two methods. In one method, the solutions in water were prepared by a vigorous stirring method followed by n-hexane extraction and GC-ECD analysis. In the second method, HPLC was used to prepare the saturated solutions. Experimental results were compared with the predictive values, the relative standard deviations are around 10%. Most of the chlorinated benzenes exhibit water induced transformations. The transformation produ… more
Date: August 1990
Creator: Wang, Hui-Wen
Item Type: Refine your search to only Thesis or Dissertation
open access

Photochemical Silaylide, Silylene and Silene Syntheses

Description: The synthesis of o-(N,N-dimethylamino)methylphenyl tris (trimethylsilyl) silane (II), a photochemical precursor of o- (N,N-dimethylamino) methylphenyl (trimethylsilyl) sila ammonium ylide (intramolecular silylene complex) and otolyl(trimethylsilyl)silylene is reported. Photolysis of II at room temperature in a cyclohexane solution of triethyl silane produced the silylene ylide and the presumably uncomplexed isomer, a silylene, which is trapped to afford the 2-(o-(N,N-dimethylamino)methylphenyl)… more
Date: August 1990
Creator: Tan, Changqing
Item Type: Refine your search to only Thesis or Dissertation
open access

Studies of Solvent Displacement from Solvated Metal Carbonyl Complexes of Chromium, Molybdenum, and Tungsten

Description: Flash photolysis techniques were applied to studies of solvent displacement by Lewis bases (L) from solvated metal carbonyl complexes of Cr, Mo, and W. On the basis of extensive studies of the reaction rate laws, activation parameters , and linear-free-energy-relationships, it was concluded that the mechanisms of solvent displacement reactions depend on the electronic and steric properties of the solvents and L, as well as the identities of the metal atoms. The strengths of solvent-metal bondin… more
Date: August 1990
Creator: Zhang, Shulin
Item Type: Refine your search to only Thesis or Dissertation
open access

A Kinetic Study of the Recombination Reacton Na + SO₂ + Ar

Description: The recombination reaction Na + S02 + Ar was investigated at 787 16 K and at pressures from 1.7 to 80 kPa. NaI vapor was photolyzed by an excimer laser at 308 nm to create Na atoms, whose concentration was monitored by time-resolved resonance absorption at 589 nm. The rate constant at the low pressure limit is ko = (2.7 0.2) x 10-21 cm6 molecule-2 s~1. The Na-SO 2 dissociation energy E0 = 170 35 kJ mol1 was calculated with RRKM theory. The equilibrium constant gave a lower limit E0 > 172 kJ mol… more
Date: December 1990
Creator: Shi, Youchun
Item Type: Refine your search to only Thesis or Dissertation
open access

Synthesis and 2-D NMR Analysis of a New Phenyl-Substituted Polycyclic Compound

Description: Diels-Alder [4+2] cycloaddition of a mixture of 1- and 2 methylcyclopentadiene to 2-phenyl-g.-benzoquinone affords a mixture of four nd cycloadducts. A single, isomerically pure cycloadduct was isolated by careful column chromatography. Stereospecific reduction of this material with sodium borohydride and cerium(III) chloride 'affords a single, isomerically pure tricyclic diol. The structures of the cycloadduct and this tricyclic diol, established via analysis of their one- and two-dimensionial… more
Date: May 1991
Creator: Tsay, Fuh-Rong
Item Type: Refine your search to only Thesis or Dissertation
open access

Comparison of 43Sn/43Pb/14Bi Solder and Standard 60Sn/40Pb Solder by Thermocyclic Fatigue Analysis

Description: The thermocyclic fatigue behavior of the low-melting solder 43Sn/43Pb/14Bi has been investigated and compared to that of standard 60Sn/4OPb solder via metallographic analysis (using scanning electron microscopy) and evaluation of the degree of fatigue development (using a fatigue scale as a function of thermocycles). Specimens were subjected to shearing strains imposed by several hundred fatigue thermocycles. Both solder types fatigue by the same microstructural failure mechanism as described b… more
Date: August 1991
Creator: Calderon, Jose Guadalupe
Item Type: Refine your search to only Thesis or Dissertation
open access

Ligand Substitution Studies in the Tetracobalt Cluster Co₄(CO)₁₀([mu]₄-PPh₂) and Synthesis and Reactivity Studies in the Fe₂Pt and FeCo₂ Mixed-metal Clusters

Description: The kinetics of ligand substitution for CO in Co4(CO)10(mu4-PPh2) , 1, have been investigated for the ligands P(OMe)3, P(OEt)3, PPh2H, P(0-i-Pr)3, P(n-Bu)3, PPh3, P(i-Pr)3, and PCy3 over a wide temperature range.
Date: August 1991
Creator: Don, Ming-jaw
Item Type: Refine your search to only Thesis or Dissertation
open access

Static and Flow Properties of Dilute Polymer Solutions

Description: Small weight percentages of certain high-molecular weight polymers added to liquids in turbulent flow through conduits can result in dramatic friction reduction. Although many current and potential uses of the drag reduction phenomenon exist, there is a fundamental problem: drag reduction efficacy decreases rapidly with flow time due to the mechanical degradation in flow of the added polymer. In this thesis study, dilute aqueous solutions of polyacrylamide were tested under turbulent flow condi… more
Date: August 1991
Creator: Whang, Kyu-ho
Item Type: Refine your search to only Thesis or Dissertation
open access

The Precipitation of Strontium Sulfate in Gels

Description: The growth of strontium sulfate precipitate by diffusion in various gels was studied by using optical transmission and confocal microscopies, scanning and transmission electron microscopies, and energy dispersive X ray fluorescence. Pure silica gel, pure agarose gel and the silica/agarose mixed gel at pH 7 - 10 were used throughout the present study. Precipitate morphology is sensitive to pH and to the nature of the growth medium. The morphology was observed as a function of time. The lack of c… more
Date: December 1991
Creator: Lee, Ya
Item Type: Refine your search to only Thesis or Dissertation
open access

Preparation and Stereochemistry of Reactive Intermediates Containing a Silicon-Carbon Double Bond

Description: 1,1-Dimethyl-2-neopentylsilene reacted with the N-methylimine of benzophenone to give 1,2,2-trimethyl-3- neopentyl-4,4-diphenyl-l-aza-2-silacyclobutane, I, and 2,3,4,4a-tetrahydro-2,3,3-trimethyl-1-phenyl-4-neopentyl-2- aza-3-silanephthalene, II, in 35% and 20% yields, respectively. Compounds I and II did not serve as thermal silene precursors. Heating I and II to over 280°C did not yield 1,3-disilacyclobutanes. In the presence of 2,3- dimethyl-1,3-butadiene typical silene products were not obt… more
Date: December 1991
Creator: Uang, Shinian
Item Type: Refine your search to only Thesis or Dissertation
open access

Raman and NMR Investigation of Molecular Reorientation and Internal Rotation in Liquids

Description: Molecular rotational motions are known to influence both Raman scattering of light and nuclear spin relaxation. Therefore, the application of Raman bandshape analysis and NMR relaxation time measurements to probe molecular dynamics in liquids will provide us with a deeper understanding of the dynamical behavior and structure of molecules in the liquid phase. Presented here are (i) studies of molecular reorientation of acetonitrile in the neat liquid phase and in solution by Raman bandshape ana… more
Date: December 1991
Creator: Yuan, Peng
Item Type: Refine your search to only Thesis or Dissertation
open access

Kinetic Studies of the Reactions of Cl and Br with Silane and Trimethylsilane

Description: The temperature dependence of the reactions of halogen atoms Cl and Br with SiH4 and (CH3)3SiH have been investigated with the flash photolysis-resonance fluorescence technique. CCI4 and CH2Br2 were used as precursors to produce Cl and Br atoms, respectively. Experiments gave {k(Cl + SiH4) (295 - 472 K)} = (1.56 +0.11) x 10-1 exp[(2.0 + 0.2) kJ mol'/RT] cm3 s4, {k(Br + SiH4)(295 - 575 K)} = (9.0 + 1.5) x 10-" exp[-(17.0 + 0.6) Id mol'/RT] cm3 s', {k(Cl + (CH3)3SiH)(295 - 468 K)} = (1.24 0.35) x… more
Date: May 1992
Creator: Ding, Luying
Item Type: Refine your search to only Thesis or Dissertation
open access

The Metal-Organic Chemical Vapor Deposition of Cu(II)-bishexafluoroacetylacetonate on a Tungsten Substrate

Description: Evidence is reported for the formation of carbon-containing contamination products at the copper-tungsten (Cu-W) interface during the metal organic chemical vapor deposition (MOCVD) of copper on tungsten. Cu(II)bishexafluoroacetylacetonate [Cu(hfac)_2] was physisorbed onto lightly oxidized tungsten (WO_x) at 115K, under ultra-high vacuum conditions, and then annealed sequentially to higher temperatures. Copper reduction was observed by 320K. Carbonaceous and carbidic contamination of the WO_x s… more
Date: May 1992
Creator: Welton, Theresa E. (Theresa Eilene)
Item Type: Refine your search to only Thesis or Dissertation
open access

Kinetic Study of the Reactions of Oxygen Atoms with Nitric Oxide and Silane

Description: The rate constant for the reactions of oxygen atoms with nitric oxide and silane were determined using a discharge flow apparatus. A microwave discharge through O2N2 and Ar was used to produce oxygen atoms. The rate constant for the reaction O + NO + Ar was determined to be (7.0+0.4) x 10^32 cm^6 s^-1 and is in good agreement with previous measurements. Modeling of the O +SiH₄ reaction was performed to determine the correction to the rate constant due to secondary reactions. The rate constant f… more
Date: August 1992
Creator: Taylor, Craig A. (Craig Allan)
Item Type: Refine your search to only Thesis or Dissertation
open access

Solution Studies of the Structures and Stability of Mixed Lithium Alkoxide/Alkvllithium Aggregates

Description: New one- and two-dimensional NMR techniques were used to elucidate the solution structures of these complex mixtures. The system, lithium tert-butoxide/tert-butyllithium, was studied as a model system with O/Li ratios varying from 0/1 to 1/1. It was found that at low O/Li ratios, a single mixed tetrameric aggregate was formed. At higher O/Li ratios, mixed hexameric species were formed. Two other systems, lithium isopropoxide/iso-propyllithium and lithium n-propoxide/n-propyllithium were also st… more
Date: December 1992
Creator: DeLong, George T. (George Thomas)
Item Type: Refine your search to only Thesis or Dissertation
open access

Thermochemical Investigation of Ternary Nonelectrolyte Mixtures

Description: Excess molar volumes have been determined for four ternary chlorobenzene + dibutyl ether + alkane mixtures at 25°C. Results of these measurements are used to test the applications and limitations of BAB, Redlich-Kister, Kohler and Hwang et al. cubic models. For the systems studied, Redlich- Kister, Kohler and Cubic models were found to provide reasonable predictions. Differences between experimental and predicted ΔV^ex_123 values were about ±0.020 cm^3mol^-1 or less at most ternary compositions… more
Date: December 1992
Creator: Teng, I-Lih
Item Type: Refine your search to only Thesis or Dissertation
open access

The Development of Predictive Models for the Acid Degradation of Chrysotile Asbestos

Description: The purpose of this study was to determine the factors affecting the acid degradation of chrysotile asbestos (Mg_3Si_2O_5(OH_4)) . Millions of tons of asbestos have found use in this country as insulative or ablative material. More than 95 percent of the asbestos in use is of the chrysotile variety. The remaining 5 percent is composed of various types of fibrous amphiboles. The inhalation of asbestos can lead to several diseases in humans. Asbestosis, lung cancer and mesothelioma are the most c… more
Date: May 1993
Creator: Ingram, Kevin D. (Kevin Dean)
Item Type: Refine your search to only Thesis or Dissertation
open access

Solderability Study of Tin/Lead Alloy Under Steam-Aging Treatment by Electrochemical Reduction Analysis and Wetting Balance Tests

Description: Two types of solder samples, pins and through-holes were tested by SERA™ (Sequential Electrochemical Reduction Analysis) and Wetting Balance after various length of steamaging treatment. It was shown that after steam-aging, both types of specimen gave a similar electrochemical reduction curve, and solderabilty predictions made from SERA™ test agree with results obtained from Wetting Balance test on a qualitative base. Wetting balance test of pin samples after SERA™ test confirmed that SERA™ is … more
Date: May 1993
Creator: Gao, Yang, 1966-
Item Type: Refine your search to only Thesis or Dissertation
Back to Top of Screen