Chemical Equilibria in Binary Solvents (open access)

Chemical Equilibria in Binary Solvents

Dissertation research involves development of Mobile Order Theory thermodynamic models to mathematically describe and predict the solubility, spectral properties, protonation equilibrium constants and two-phase partitioning behavior of solutes dissolved in binary solvent mixtures of analytical importance. Information gained provide a better understanding of solute-solvent and solvent-solvent interactions at the molecular level, which will facilitate the development of better chemical separation methods based upon both gas-liquid and high-performance liquid chromatography, and better analysis methods based upon complexiometric and spectroscopic methods. Dissertation research emphasizes chemical equilibria in systems containing alcohol cosolvents with the understanding that knowledge gained will be transferable to more environmentally friendly aqueous-organic solvent mixtures.
Date: August 1997
Creator: McHale, Mary E. R.
System: The UNT Digital Library
Synthesis and Characterization of Methylated PCU Dimers (open access)

Synthesis and Characterization of Methylated PCU Dimers

Conversion of 1-Methylpentacyclo[5.4.0.0²⋅⁶.0³⋅¹⁰.0⁵⋅⁹]undecane- 8,11-dione into the corresponding mono(ethylene ketal) followed by Wolff-Kishner reduction resulted in a mixture of two isomers (i.e., 1- and 7-methyl-8-[2',-(1',3',dioxolano)]pentacyclo[5.4.0.0²⋅⁶.0³⋅¹⁰.0⁵⋅⁹] undecane. Hydrolysis of each isomer in turn resulted in 1- and 7- methyl pentacyclo[5.4.0.0²⋅⁶.0³⋅¹⁰.0⁵⋅⁹ ]undecan-8-ones (i.e.,"methylated PCU-8-ones"), respectively. "Titanium-promoted reductive dimerization of each of the methylated pentacycloundecane (PCU)-8-ones afforded mixtures of "methylated PCU alkene dimers". Individual isomers have been isolated from these mixtures via column chromatography by using silver nitrate impregnated silica gel as adsorbent followed by fractional recrystallizations of individual chromatography fractions. Structures of three isomerically pure methylated PCU alkene dimers (C₂₄H₂₈) have been established unequivocally by application of single crystal X-ray crystallographic methods.
Date: August 1993
Creator: Zope, Anjali U. (Anjali Umesh)
System: The UNT Digital Library
Photochemical Silaylide, Silylene and Silene Syntheses (open access)

Photochemical Silaylide, Silylene and Silene Syntheses

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) -1,1,1-triethyl 3,3,3-trimethyltrisilane, 33% yield. A second decomposition pathway, a photodeamination, produced o-tris(trimethyl silyl) silyltoluene. UV spectra of the silaammonium ylide formed in the photochemical reaction of II was observed at 77k in hard or soft matrices.
Date: August 1990
Creator: Tan, Changqing
System: The UNT Digital Library
Aqueous Solubilities and Transformation of Chlorinated Benzenes (open access)

Aqueous Solubilities and Transformation of Chlorinated Benzenes

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 products were either isomeric or with higher and lower numbers of chlorine substituents. The transformation phenomena can be explained by polarity, symmetry, reactivity of the chlorine atoms, and hydrophobic interactions. The mechanism of the transformation is governed by the radical mechanism.
Date: August 1990
Creator: Wang, Hui-Wen
System: The UNT Digital Library
Kinetic Study of the Reactions of Oxygen Atoms with Nitric Oxide and Silane (open access)

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

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 for the reaction O + SiH₄ was determined to be (3.3 +/- 0.3) x 10⁻¹³ cm³ s⁻¹ and is in good agreement with previous measurements. Previous literature, thermochemistry, and spin conservation were used to determine a probable mechanism for the O + SiH₄ reaction.
Date: August 1992
Creator: Taylor, Craig A. (Craig Allan)
System: The UNT Digital Library
Comparison of 43Sn/43Pb/14Bi Solder and Standard 60Sn/40Pb Solder by Thermocyclic Fatigue Analysis (open access)

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

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 by other workers. The mechanism is characterized by a preferential coarsening of the solder joint microstructure at the region of maximum stress concentration where cracks originate.
Date: August 1991
Creator: Calderon, Jose Guadalupe
System: The UNT Digital Library