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 Degree Discipline: Chemistry
Synthesis of Gold Complexes From Diphosphine Ligands and Screening Reactions of Heterocyclic Acetylacetonato (Acac) Ligands with Transitional Metal Complexes
Syntheses of diphosphine gold (I) complexes from gold THT and two ligands, 4, 5-bis (diphenylphosphino)-4-cyclopenten-1, 3-dione (BPCD) and 2,3-bis(diphenylphosphino)-N-phenylmaleimide (BPPM), were done separately. The reactions happened under ice conditions followed by room temperature conditions and produced two diphosphine gold (I) complexes in moderated yield. Spectroscopic results including nuclear magnetic resonance (NMR) and X-ray crystallography were used to study and determine the structures of the products formed. Moreover, X-rays of all newly synthesized diphosphine gold (I) complexes were compared with the known X-ray structures of other phosphine and diphosphine gold (I) complexes. There were direct resemblances in terms of bond length and angle between these new diphosphine gold (I) complex structures and those already published. For instance, the bond lengths and angles from the newly prepared diphosphine gold (I) complexes were similar to those already published. Where there were some deviations in bond angles and length between the newly synthesized structures and those already published, appropriate explanation was given to explain the deviation. Heterocyclic ligands bearing acetylacetonate (ACAC) side arm(s) were prepared from ethyl malonyl chloride and the heterocyclic compounds 8-hydroxylquinoline, Syn-2-peridoxyaldoxime, quinoxalinol and 2, 6-dipyridinylmethanol. The products (heterocyclic ACAC ligands) from these reactions were screened with transition metal carbonyl compounds in thermolytic reactions. The complexes formed were studied and investigated using NMR and X-ray crystallography. Furthermore, the X-ray structures of the heterocyclic ACAC ligand or ligand A and that of rhenium complex 1 were compared with similar published X-ray structures. The comparison showed there were some similarities in terms of bond length and bond angles. digital.library.unt.edu/ark:/67531/metadc804890/
Applications of Single Reference Methods to Multi-Reference Problems
Density functional theory is an efficient and useful method of solving single-reference computational chemistry problems, however it struggles with multi-reference systems. Modifications have been developed in order to improve the capabilities of density functional theory. In this work, density functional theory has been successfully applied to solve multi-reference systems with large amounts of non-dynamical correlation by use of modifications. It has also been successfully applied for geometry optimizations for lanthanide trifluorides. digital.library.unt.edu/ark:/67531/metadc801919/
Computational Studies of C–h/c–c Manipulation Utilizing Transition Metal Complexes
Density Functional Theory (DFT) is an effective tool for studying diverse metal systems. Presented herein are studies of a variety of metal systems, which can be applied to accomplish transformations that are currently difficult/impossible to achieve. The specific topics studied utilizing DFT include: 1) C–H bond activation via an Earth-abundant transition metal complex, 2) C–H bond deprotonation via an alkali metal superbase, 3) and amination/aziridination reactions utilizing a CuI reagent. Using DFT, the transformation to methanol (CH3OH) from methane (CH4) was examined. The transition metal systems studied for this transformation included a model FeII complex. This first-row transition metal is an economical, Earth-abundant metal. The ligand set for this transformation includes a carbonyl ligand in one set of complexes as well as a phosphite ligand in another. The 3d Fe metal shows the ability to convert alkyls/aryls to their oxidized counterpart in an energetically favorable manner. Also, “superbasic” alkali metal amides were investigated to perform C—H bond cleavage. Toluene was the substrate of interest with Cs chosen to be the metal of interest because of the highly electropositive nature of this alkali metal. These highly electrophilic Cs metal systems allow for very favorable C—H bond scission with a toluene substrate. Finally, the amination and aziridination of C–H and C=C bonds, respectively, by a CuI reagent was studied. The mechanism was investigated using DFT calculations. Presently, these mechanisms involving the use of coinage metals are debated. Our DFT simulations shed some insight into how these transformations occur and ultimately how they can be manipulated. digital.library.unt.edu/ark:/67531/metadc801892/
Quantitative Chemical Analysis of the Soils of Erath County, Texas
A chemical analysis of representative samples of Windthorst sand, Denton sand, and Denton clay has been made, and this analysis shows that their composition has a strict correlation with respect to their geological origins. The analyses of the different soils have shown the Windthorst sand to be highly deficient in all of the essential elements, whereas the Denton sand is deficient in only one; namely, phosphorus. The analysis of the Denton clay showed it to be highly fertile. From the consideration of the pH and the lime content, it has been determined to some extent what crops will grow in each of the soils. digital.library.unt.edu/ark:/67531/metadc699523/
A Study of the Quantitative Determination of Nitrogen
The purpose of this paper is to investigate the Kjeldahl method of nitrogen determination. digital.library.unt.edu/ark:/67531/metadc699658/
The Correlation Between Carbon-Proton and Proton-Proton Coupling Constants
The correlation between the carbon-proton and proton-proton coupling constants have been studied in various 13 systems. Isocrotonic acid-carboxyl-3C, crotonic acid- 13 13 carboxyl-3C, and 5-norbornene-2-carboxylic acid-carboxyl-3C- 1,5,6,7,7-hexachloro were synthesized and their carbonproton coupling constants were analyzed. Nmr studies showed the magnitudes of the carbon-proton coupling constants to correlate well with analogous protonproton coupling constants, although the values of the couplings were larger than expected. The geminal olefinic couplings were considerably larger than all other couplings, but they were self-consistent. The signs of the carbon-proton coupling constants also were in agreement without exception with the signs of analogous proton-proton coupling constants. digital.library.unt.edu/ark:/67531/metadc663212/
Chemical Cleavage of Human Phosphoglucose Isomerase at Cysteine
The present study has resulted in the development of a procedure for the specific chemical fragmentation of human phosphoglucose isomerase into a minimal number of peptides. A two-cycle procedure for cleaving the protein with 2-nitro-5- thiocyanobenzoic acid results in four primary peptides and three overlap peptides. The peptides can be readily separated on the basis of their size by using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Preliminary peptide alignments have been considered, and amino acid analyses have been performed. End-terminal analyses of the enzyme revealed a carboxyl terminal sequence of Asp-Val-Gln and a blocked amino terminus. The cysteine cleavage procedure provides an excellent method for the identification and location of specific genetic mutations of human phosphoglucose isomerase. digital.library.unt.edu/ark:/67531/metadc663679/
Magnetic Properties of Metal(II) Schiff Base Complexes
Ligands prepared from various combinations of aldehydes and ketones with the appropriate aminealcohol were complexed with cupric acetate monohydrate. The complexes with O,NO or N,N,O donor atoms were synthesized to study the influences of the ligand on molecular structure, spin-spin interaction, and on the value of the exchange integral. The magnetic data indicated that of the eight Cu(II) complexes discussed, two behaved differently from known analogous compounds. Cu (benzoylacetone :ethanolamine) was compared to Cu(acac:ethanolamine), and Cu(pyrr:oaminophenol) was compared to Cu(acac:o-aminophenol). Each pair of complexes was postulated to have the same molecular structure. The synthesis and characterization of Mn(pyrr:oaminophenol) 2H2 is also discussed. The following physical data were collected and discussed: elemental analysis, melting point, molecular weight, infrared spectra, electronic spectra, and magnetic susceptibility. digital.library.unt.edu/ark:/67531/metadc663278/
Synthesis and Study of Glutaryl-S-(ω-aminoalkyl)-L-cysteinylglycines as Inhibitors of Glyoxalase I
This thesis describes the synthesis and preliminary enzymatic study of glutaryl-S-(8-aminooctyl)-L-cysteinylglycine and glutaryl-S-(10-aminodecyl)-L-cysteinylglycine as inhibitors of glyoxalase I. These analogs of glutathione were prepared as potential ligands for affinity chromatography purification of glyoxalase I. The compounds were synthesized by a seven-step procedure in overall yields of 24% for the octyl analog and 33% for the decyl analog. Both compounds exhibited mixed type inhibition of the enzyme, with the decyl derivative being more inhibitory than the octyl derivative. The inhibition was nonlinear (parabolic) for both compounds. Although less inhibitory than the corresponding S-substituted glutathione derivatives, these analogs are promising candidates for affinity chromatography ligands. Such compounds may also be useful in studying the mechanism of glyoxalase I. digital.library.unt.edu/ark:/67531/metadc663491/
Magnetic Properties of Copper (II) Complexes of Schiff Bases
The synthesis and characterization of two new Schiff base copper(II) complexes are reported. These are Cu(acac: 2-amino-l-phenylethanol) and Cu(acac:2-amino-l-butanol). The ligands, derived from acetylacetone and the appropriate aminoalcohol, are dibasic tridentates with 0,N,O donor atoms. The magnetic properties of the complexes were studied at several temperatures between 78 OK and 296 OK. The magnetic moment of Cu(acac:2-amino-l-phenylethanol) varied little with temperature, and that of Cu(acac:2-amino-lbutanol) increased as the temperature was lowered. This is in contrast to the magnetic moment of Cu(acac:ethanolamine), which decreases as the temperature decreases. Molecular weight data, infrared spectra, magnetic data, electronic spectra, and electron spin resonance spectra of both complexes are reported and discussed. digital.library.unt.edu/ark:/67531/metadc663734/
Copper (II) Complexes with Deprotonated N-(2-hydroxyethyl)ethylenediamine
This thesis reports the synthesis and characterization of two new copper(II) halide complexes with deprotonated N-(2-hydroxyethyl)ethylenediamine behaving as a bidentate. The magnetic properties of the new copper(II) complexes were studied from room temperature to liquid nitrogen temperatures. The magnetic data show that both complexes exhibit antiferromagnetic interactions with a singlet ground state and a thermally accessible triplet excited state. Magnetic data and infrared spectra indicate the complexes are halogenbridged. Deprotonation at an amine nitrogen is based on the presence of a hydroxyl stretching band in the infrared spectra. Electronic spectra and infrared spectra indicate the complexes are square planar. Elemental analyses, infrared spectra, electronic spectra, electron spin resonance spectra, and magnetic data are reported and discussed. digital.library.unt.edu/ark:/67531/metadc663729/
Denaturation, Renaturation and Other Structural Studies on Phosphoglucose Isomerases
Structural properties of phosphoglucose isomerases isolated from a variety of species have been compared by peptide fingerprinting, predicted amino acid sequence homologies and by denaturation and renaturation studies. The enzymes are more readily denatured in guanidinium chloride than in urea, and the isomerase isolated from yeast is more stable toward acid pH than the rabbit muscle enzyme. The rates of guanidinium chloride-induced denaturation are markedly increased by ionic strength and decreased by substrates, competitive inhibitors or glycerol. The enzyme can be renatured, but only in the presence of glycerol. The renaturation process is dependent on protein concentration and temperature and provides a method for the formation of mixed species heterodimers. digital.library.unt.edu/ark:/67531/metadc663054/
Studies of L-Asparaginase from Lactobacillus Plantarum
This study is concerned with the regulation of Lasparaginase (LA) in the cell-free crude extracts from Lactobacillus plantarum (ATCC8014). A previously reported finding that adenosine triphosphate (ATP) inhibits the action of LA in crude extracts was confirmed. The study was extended to include the mono-, di-, and triphosphates of adenosine, guanosine, cytidine, and uridine. These compounds were also shown to inhibit LA activity. These andother studies revealed that LA appears to be an allosteric type enzyme exhibiting positive homotropism with respect to substrate and heterotropism with respect to the nucleotides tested. The regulation of LA activity by high energy compounds, when coupled with asparagine synthetaseL suggests a relationship between amide synthesis-amide degradation and the energy levels of the cell. digital.library.unt.edu/ark:/67531/metadc663296/
Isolation and Characterization of Proteus vulgaris Methylglyoxal Synthetase
Methylglyoxal synthetase, which catalyzes the formation of methylglyoxal and inorganic phosphate from dihydroxyacetone phosphate, was found in extracts of Proteus vulgaris. An efficient purification procedure utilizing ion exchange column chromatography and isoelectric focusing has been developed. Homogeneity of the enzyme preparation was confirmed by polyacrylamide gel electrophoresis and rechromatography.Two components of methylglyoxal synthetase were obtained upon isoelectric focusing. A comparison of the chemical and physical properties of the two components was carried out. The enzyme is a dimer. In the presence of inorganic phosphate, the hyperbolic saturation kinetics with dihydroxyacetone phosphate are shifted to sigmoidal. digital.library.unt.edu/ark:/67531/metadc663809/
The Crystal and Molecular Structure of 2, 2' bipyridylglycinatochloro Copper (II) Dihydrate
The three-dimensional x-ray structure of 2,2'-bipyridylglycinatochloro copper(II) dihydrate has been fully refined to a final R factor of 0.081. The bipyridyl and glycine ligands are arranged about the central copper atom in a square planar configuration while the chlorine atom is 2.635 angstroms above this plane directly over the copper atom. This unusually long distance is explained by the positioning of a glycine group on the opposite side of the square plane, resulting in a distorted octahedral arrangement. Also, the chlorine atom is linked to three oxygen atoms via hydrogen bonding, thus stabilizing the distorted octahedral complex. digital.library.unt.edu/ark:/67531/metadc663591/
The Vacuum Ultraviolet Spectra of Cyclohexane, Cyclohexene, 1,4-Cyclohexadiene, Isotetralin, and Several Methyl Substituted Analogs
A paucity of literature exists on the Independent System analysis of adjacent, parallel transition dipoles. Applying this theory and certain spectral information semiemperical calculations were made to predict absorption profiles and band intensities. To aid in the assignment of the 7*+7 absorption bands it was necessary to obtain the vacuum ultraviolet spectra of cyclohexane and cyclohexene. Because the spectra of these molecules contained sharp, atomic-like absorption bands a Rydberg series could be fitted to certain absorptions, thus the determination of their ionization potentials. Using Independent System analysis profiles and intensities of 7*+q-- absorption bands ins 'several methyl substituted 1,4- cyclohexadienes and isotetralin were predicted where general agreement was found with observed experimental spectra. digital.library.unt.edu/ark:/67531/metadc663526/
Inhibitors of Dihydrofolate Reductase, 8-Oxapteridines
The biological activities of some homeosterically related analogs of dihydrofolic acid have been examined involving pyrimido[4,5-b][l,4]oxazine (8-oxapteridine) derivatives. It is anticipated that these compounds might interfere with the essential intermediary metabolic functions of the vitamin and thus serve as potential chemotherapeutic agents. Preliminary toxicity studies in microbial assay systems were disappointing; however, inhibitory effects were demonstrated in cell free enzyme systems. A comparison of the structure/activity relationships was determined using two folic acid coenzyme systems, dihydrofolate reductase and thymidylate synthetase. The 2-amino-4-hydroxy-6-(substituted)-8-oxapteridines were generally more effective inhibitors than the corresponding 2,4-diamino analogs. The relative biological activity of a series of 2-amino-4-hydroxy-6-ω-phenylalkyl derivatives were examined, and the most active derivative was the 6-phenylethyl analog which appears to function as a mixed-type inhibitor involving partially competitive and partially non-competitive inhibition. digital.library.unt.edu/ark:/67531/metadc663439/
Studies Concerning Asparagine Metabolism in Lactobacillus plantarum
This study is concerned with the metabolism of L-asparagine in Lactobacillus plantarum (ATCC 8014). Theprimary area of investigation is the preliminary characterization of a previously unreported L-asparaginase enzyme in L. plantarum. This L-asparaginase was determined to be an inducible enzyme with variations in its activity level according to the L-asparagine level in the growth medium. L-Glutaminase could not be induced in this organism by L-glutamine, nor would L-glutamine induce the asparaginase activity. These and other studies with amino acid analogs demonstrated the high specificity of both induction and enzymic activity of the asparaginase. Various physical properties of the enzyme were studied. The enzyme was found to be inhibited by adenosine triphosphate (ATP). This inhibition appears to be cooperative in nature and of the type exhibited by allosteric enzymes. These studies should be confirmed on a highly purified enzyme as these preliminary experiments were performed using a crude cell-free extract. digital.library.unt.edu/ark:/67531/metadc663794/
Isozymes and In Vivo Activity of Triosephosphate Isomerase
The distribution of isozymes of triosephosphate isomerase was normal in all human tissues examined. This finding argues against the existence of tissue-specific isozymes. Normal distributions of isozymes were also found in patients with cri-du-chat syndrome. Thus it is unlikely that a gene for triosephosphate isomerase is located on the short arm of chromosome five in man. When triosephosphate isomerases from a wide range of species were examined by starch gel electrophoresis, definite evolutionary patterns were found. Kinetic studies were conducted on human triosephosphate isomerase under conditions simulating the intracellular environment of the erythrocyte. Calculations using the kinetic parameters obtained indicate that even in triosephosphate isomerase deficiency disease, enough enzyme activity remains that the rate of glycolysis should not become inhibited. digital.library.unt.edu/ark:/67531/metadc663801/
The Electronic Spectrum of (-)-S-(pS)-2,5,3',6'-Tetrahydro-2.2-Paracyclophane-2-Carboxylic Acid
A new, efficient route was used in the synthesis of [2.2]-paracyclophane-2-carboxylic acid. The acid as then resolved and the Birch reduction performed yielding one enantiomer of tetrahydro-[2.2]-paracyclophane-2-carboxylic acid. The ultraviolet spectrum of tetrahydro-[2.2]-paracyclophane- 2-carboxylic acid in isopenthane shows one absorption at 206 nm (Emax = 5,271). There are three bands observed in the circular dichroism spectrum in isopentane at 236 nm ([] = 1.8 X 104), 201 nm ([0] = -16 X 104) and a positive band indicated below 180 nm but not observed. The bands were assigned and possible reasons for the occurrence of a mr'r* transition at unexpectedly long wavelengths are discussed. digital.library.unt.edu/ark:/67531/metadc504545/
The Chlorination of Amino Acid in Municipal Waste Effluents
In model reaction systems to test amino acids in chlorinated waste effluents, several amino acids were chlorinated at high chlorine doses. (2000-4000 mg/1). Amino acids present in municipal waste effluents before and after chlorination were concentrated and purified using cation exchange and Chelex resins. After concentration and cleanup of the samples, the amino acids were derivatized by esterification of the acid functional groups and acylation of the amine groups. Identification and quantification of the amino acids and chlorination products was carried out by gas chromatography/mass spectrometry, using a digital computer data system. Analysis of the waste products revealed the presence of new carbon-chlorine bonded derivatives of the amino acid tyrosine when the effluents were treated with heavy doses of chlorine. digital.library.unt.edu/ark:/67531/metadc504631/
Regulation of Pyridine Nucleotide Metabolism in Saccharomyces cerevisiae
The levels of total nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), and their redox states were determined as the function of growth in S. cerevisiae. Cells growing in a medium containing 0.8% glucose exhibit two phases of exponential growth, utilizing glucose and ethanol, respectively. The NAD pool is 50% reduced during both stages of growth while the NADP pool is 67% reduced in glucose growth and 48% reduced in ethanol growth. The NAD/NADP ratio is constant during growth on glucose and a two-fold increase in the NAD/NADP ratio occurs upon exhaustion of glucose. The increased ratio is maintained during growth on ethanol. This alteration in the regulation of the relative levels of NAD and NADP may be due to a change in the regulation of NAD kinase and/or NADP phosphatase activities. These changes may be related to the redox state of the NADP pool. digital.library.unt.edu/ark:/67531/metadc504002/
The Determination of Organic-Bound Chlorine Levels in Municipal Wastewaters After Treatment with Heavy Chlorine Doses
The development of an analytical method for the determination of total organic-bound chlorine (TOCl) produced during the chlorination of municipal wastewater effluents is presented. Sewage effluent from the Denton, Texas municipal treatment plant was chlorinated at high chlorine doses (1000 - 4000 ppm), as well as typical treatment levels. Chlororganics present in the wastewater, before and after chlorination, were concentrated by adsorption on Amberlite XAD-2 macroreticular resin, followed by elution with diethyl ether. After concentration, the extracts were analyzed for TOC1 by microcoulometry. Analysis of wastewater extracts revealed the production of substantial amounts of new chlorinated organics when effluents were treated with chlorine. The method shows good precision and estimated accuracy is favorable. digital.library.unt.edu/ark:/67531/metadc504486/
Structure, Energetics and Reactions of Bisketenes: An Ab Initio and Density Functional Theory Study
The effect of varying substituents on structure and energies of bisketenes was studied using ab initio methods. Effect of substituents on ring closing reaction of bisketenes to the corresponding cyclobutenediones was also studied using ab initio methods. One or two of the following substituents were used to study the effect of varying substituents: BH2, CH3, NH2, OH, F, AlH2, SiH3, PH2, SH, Cl. Studies were done at the Hartree-Fock (HF), Møller-Plesset (MP2), and Density Functional Theory (B3LYP) levels of theory using the 6-31G* basis set. digital.library.unt.edu/ark:/67531/metadc501272/
Reduction Pathways in Cyclopentadienyl Rhenium Dicarbonyl Dibromide Deriviatives and Indenyl Rhenium Tricarbonyl: Synthesis, Structure, and Reactivity of Anionic Cyclopentadienyl Rhenium Complexes. Ring Attack vs. Metal-Halogen Exchange
The reactions of diagonal and lateral Cp'Re(CO)2Br2 (where Cp' = n5-C5H5, n5-C5Me5) and (n5-CgH7)Re(CO)3 with reducing agents have been examined. Hydride reduction at -78 °C is observed to occur at the Cp ring in both CpRe(CO)2Br2 isomers, affording a thermally unstable [(n4 -C5Hg)Re(CO)2Br2]- complex. The product of hydride ring attack has been characterized by low-temperature IR and 1H NMR measurements in addition to 13C NOE and heteronuclear 2D NMR measurements. Reaction of lateral CpRe(CO)2Br2 with either MeLi or PhLi affords both Cp-ring attack and metalhalogen exchange, [CpRe(CO)2Br]- (1) while t-BuLi reacts exclusively via metal-halogen exchange. diag-CpRe(CO)2Br2 reacts with the above lithium reagents to yield the same metal-halogen exchange anion. Analogous reactions using diag- and lat-Cp*Re(CO)2Br2 (where Cp* = n5-CgMe5) afford only the corresponding rhenium metal-halogen exchange anion, [Cp*Re(CO)2Br] (2). The molecular structures of 1-[Li/15-Crown-5] and 2-PPP were established by X-ray crystallography. 1-[Li/15-Crown-5] crystallizes in the monoclinic space group P21 with a = 10.860(4) A, b = 13.116(5) A, c = 7.417(3) A, B = 105.26(3)0, V = 1018.7(3) A3 , and Z = 2. 2-PPP crystallizes in the orthorhombic space group Pbca with a = 20.646(5) A, b = 17.690(5) A, c = 17.553(3) A, and z = 8. Solution FT-IR studies of 2 in THF reveal the presence of only solvent-separated ion pairs when the gegencation is Li+, K+, or PPP+ from -70 °C to room temperature. 2-Na at room temperature displays a 39:61 mixture of carbonyl oxygen-sodium and solvent-separated ion pairs, respectively. These ion pairs reveals a reversible temperature-dependent equilibrium. The equilibrium constant has been determined by IR band shape analysis over the temperature range -70 °C to room temperature and values of AH and AS are reported. The reaction of the ring-attacked complex, diag-[(n4-C5H6)Re(CO)2Br2]- with PPh3, P(OPh)3, or Me3CNC leads to the formation of the CpRe(CO)2L. Treatment of [Cp'Re(CO)2Br]- with methyltriflate, TFA, and magic ethyl yields the corresponding diag-Cp'Re(CO)2Br(R) (R = CH3, H, C2H5) complexes based on in situ IR analysis. All of these functionalized complexes decomposed in solution over a period of days to give Cp'Re(CO)3 as the only isolable product (20-30 %). The reaction of the [Cp,Re(C0)2Br]- with Bu3SnH at 60 °C leads to the formation of diag-Cp'Re(CO)2(SnBu3)2, which was also synthesized independently by the deprotonation of diag-Cp'Re(CO)2H2 with Et3N in the presence of Bu3SnBr at room temperature. The reaction of Cp'Re(CO)2Br2 with Bu3SnH at room temperature was discovered to afford the dihydride in excellent yield and, thus represents an improved synthetic route for the synthesis of diag-Cp'Re(CO)2H2. The hydride reduction of (n5-CgH7)Re(CO)3 at room temperature leads to the immediate formation of [(n5-CgH7)Re(CO)2H]- complex, which has been characterized by IR analysis and 1H and 13C NMR spectroscopy. digital.library.unt.edu/ark:/67531/metadc332212/
Thermal and Flash Photolysis Studies of Ligand-Exchange Reactions of Substituted Metal Carbonyl Complexes of Cr and Mo
Thermal and flash photolysis studies of ligand-substitution reactions of cis-(pip)(L)M(CO)_4 by L' (pip = piperidine; L, L' = CO, phosphines, phosphites; M = Cr, Mo) implicate square-pyramidal [(L)M(CO)_4], in which L occupies a coordination site in the equatorial plane, as the reactive species. In chlorobenzene (= CB) solvent, the predominant species formed after flash photolysis and a steady-state intermediate for the thermal reaction is cis—[(CB)(L)M(CO)_4], for which rates of CB-dissociation increase with increasing steric demands of coordinated L. Rates of CB-dissociation from trans-[(CB)(L)M(CO)_4] intermediates, formed after photolysis but not thermally, exhibit no observable dependence on the steric properties of the coordinated L. digital.library.unt.edu/ark:/67531/metadc332097/
Kinetics Studies of Substituted Tungsten Carbonyl Complexes
Thermal reactions and flash photolysis are used to study the olefin bond-migration promoted by tungsten carbonyls. Substitution of piperidine (pip) by 2- allylphenyldiphenylphosphine (adpp) in the cis-(pip)(η^1- adpp)W(CO)-4 complex was investigated, and no olefin bond-migration was observed. This suggests that a vacant coordinated site adjacent to the coordinated olefin is an essential requirement for olefin bond rearrangement. The rates of olefin attack on the photogenerated coordinatively unsaturated species, cis-[(CB)(η^1-ol- P)W(CO)-4] (CB = chlorobenzene, p-ol = Ph-2P(CH-2)-3CH=CH-2; n = 1-4) were measured. Kinetics data obtained both in pure CB and in CB/cyclohexane mixtures support a dissociative mechanism in which the W-CB bond is broken in the transition state. In contrast to results observed in studies of other related systems, no olefin bond-migration is noted. This observation is attributed to P-W coordination at all stages of the reaction, which precludes formation of a reactive intermediate containing a vacant coordination site adjacent to a P-ol bond. digital.library.unt.edu/ark:/67531/metadc330797/
Studies of Nitrogen-containing Compounds Having Pyrethroid-like Bioactivity
During recent years most of the successful developments in pyrethroids have been primarily concerned with structural or compositional variations. As a part of our continuing interest in pyrethroid insecticides, nitrogen-containing compounds having pyrethroid-like structures were synthesized. Seven prolinate compounds, N-(substituted)-phenyl-prolinates and N-carbobenzoxy-prolinates were coupled with known pyrethroid alcohols. These structural variations which "locked in" a specific conformation between the nitrogen and chiral a-carbon in the acid moiety of fluvalinate were studied to determine the influence of certain conformations on insecticidal toxicity. The toxicity data for the prolinate compounds showed intermediate mortality against nonresistant cockroaches. It was concluded that the conformation imposed by the proline ring portion of the esters was probably close to the favored conformation for interaction of fluvalinate-like pyrethroids with the insect receptor site. A second series of nitrogen-containing compounds, twenty-five carbamate esters resulting from the condensation of N-isopropyl-(substituted)-anilines and N-alkyl-(substituted)-benzylamines with appropriate pyrethroid alcohols were studied for insecticidal activity. These studies were conducted on pyrethroid-susceptible houseflies. Some of the carbamate esters exhibited high toxicity when synergized by piperonyl butoxide. For example, the toxicity ( LD 50 ) of O-a-cyano-3-phenoxyfaenzyl-N-a,a-dimethyl-4-bromo-benzyl carbamate was 0.012 ug/g, which is significantly greater than that reported for the potent pyrethroid, fenvalerate. Correlations of insecticidal activity with respect to structure and conformational factors of the carbamate esters have been made. The N-isopropyl substituent decreases insecticidal activity in the N-benzyl-derived compounds, while the N-isopropyl substituent enhances activity in the N-phenyl-derived compounds. Certain substituents on the phenyl ring of both analogs greatly affect insecticidal potency of the carbamate esters. Also, some alkyl substituents (especially, a,cx-dimethyl and a-cyclopropyl groups) on the benzylic carbon of the benzylamine series enhance toxicity. The a,a-dimethyl branching of the N-benzyl carbamate approximates the steric shape given by the gemdimethyl group for conventional cyclopropane ring-containing pyrethroids. The N-benzyl compounds are significantly synergized by piperonyl butoxide, particularly those in which the carbamate nitrogen atom is mono-substituted. digital.library.unt.edu/ark:/67531/metadc332332/
Thermal Reactions of Four-Membered Rings Containing Silicon or Germanium
The synthesis of E- and Z-1,1,2,3-tetramethylsilacyclobutanes is described. Pyrolysis of either isomer at 398.2 °C provides the same products but in different amounts: propene, E- and Z-2-butene, allylethyldimethylsilane, dimethylpropylsilane, the respective geometric isomers, 1,1,2,3,3-pentamethyl-1,3-disilacyclobutane, 1,1, l-ethyldimethyl-2,2,2-vinyldimethyl-disilane and E- and Z-1,1,2,3,3,4-hexamethyl-1,3-disilacyclobutane. Mechanisms involving di- and trimethylsilenes are described for disilane formation and rate constants of the elementary steps for the fragmentation reactions are reported. Photochemically generated dimethylsilylene in the hydrocarbon solution inserts into the cyclic Ge-C or Si-C bonds of 1,1-dimethylgerma- or silacyclobutane to produce 1-germa-2-sila- or 1,2-disilacyclopentane. The relative reactivities of 1,1-dimethylgerma- and silacyclobutanes toward the dimethylsilylene have been determined. The carbenoid resulting from the cuprous chloride catalyzed decomposition of diazomethane at 25 °C in cyclohexane reacts with 1,1-dimethylgermacyclobutane to give, surprisingly 1,1,5,5-tetramethyl-1,5-digermacyclooctane as the major product. The reactions of the carbenoid with 1,1-dimethylsilacyclobutane are described. The kinetics of gas phase thermal decomposition of 1,1-dimethylgermacyclobutane has been studied over the temperature range, 684 - 751 K at pressures near 14 Torr. The Arrhenius parameters for the formation of ethylene are k_1 (s^-1) = 10^(14.6 ± 0.3) exp (62.7 ± 2.9 kcal mol^-1/RT) and those for the formation of propene and cyclopropane are k_2 (s^-1) = 10^(14.0 ± 0.1 ) exp (60.4 ± 2.8 kcal mol^-1/RT). Static gas phase pyrolyses of 1,1-dimethyl-lsilacyclobutene, DMSCB, in the presence of a variety of alkenes and alkynes at 260 - 365 °C have been studied. Our experimental results suggest that under these conditions the DMSCB ring opens to 1,1-dimethyl-l-silabutadiene, which either recyclizes to DMSCB or reacts with alkenes or alkynes in competing 4 + 2 and 2 + 2 cycloadditions. digital.library.unt.edu/ark:/67531/metadc330607/
Intramolecular [2+2] Cycloadditions of Phenoxyketenes and Intermolecular [2+2] Cycloadditions of Aminoketenes
One objective of this study was to explore the intramolecular [2+2] cycloadditions of phenoxyketenes to carbonyl groups with isoflavones and benzofurans as target compounds. The other objective was to investigate the eyeloaddition reactions of rarely studied aminoketenes. The conversion of 2-(carboxyalkoxy)benzils to the corresponding phenoxyketenes leads to an intramolecular [2+2] cycloaddition to ultimately yield isoflavones and/or 3-aroylbenzofurans. The product distributions are dependent upon the substitution pattern in the original benzil acids. The initial cycloaddition products, β-lactones, are isolated in some instances while some β-lactones spontaneously underwent decarboxylation and could not be isolated. The ketene intermediate was demonstrated in the intramolecular reaction of benzil acids or ketoacids with sodium acetate and acetic anhydride. It is suggested that sodium acetate and acetic anhydride could serve as a source for the generation of ketenes directly from certain organic acids. The treatment of ketoacids with acetic anhydride and sodium acetate provides a simpler procedure to prepare benzofurans than going through the acid chloride with subsequent triethylamine dehydrochlorination to give the ketenes. N-Ary1-N-alkylaminoketenes were prepared for the first time from the corresponding glycine derivatives by using p-toluenesulfonyl chloride and triethylamine. These aminoketenes underwent in situ cycloadditions with cyclopentadiene, cycloheptene and cyclooctenes to yield only the endo -bicyclobutanones. The cycloheptene and cyclooctene cycloaddition products underwent dehydrogenation under the reaction conditions to yield bicycloenamines. A mechanism is proposed for this dehydrogenation involving a radical cation of the arylalkylamine. (N-Phenyl-N-methyl) aminomethylketene was also prepared and found to undergo an intramolecular Friedel-Crafts type acylation to yield an indole derivative when prepared by the acetic anhydride, sodium acetate method. The in situ cycloaddition of N-aryl-N-alkyl aminoketenes with various imines was found to form predominately cis-3-amino-2-azetidinones. A mechanism involving a dipolar intermediate is provided whereby the structure of the intermediate is determined by both electronic and steric effects. The stereochemistry of the resulting β-lactams is dependent upon the structure of the dipolar intermediate. digital.library.unt.edu/ark:/67531/metadc332334/
Pyrolysis Capillary Chromatography of Refuse-Derived Fuel and Aquatic Fulvic Acids
Pyrolysis-capillary gas chromatography combined with FID, ECD and MS detection were used to characterize refuse-derived fuel and aquatic fulvic acids. Different pyrolysis methods and programs were evaluated. Pyrolysis temperatures of 700-800°C produced the strongest signal for organics present in RDF and fulvic acid. Cellulose and fatty acids pyrolyzates were identifiable by GC-MS following preparative pyrolysis fractionation. At organic chloride content of 0.023%, only three halogenated compounds were detected in the GC-MS of the fractions. None of the priority pollutants were detected at lower detection limit of 0.72 to 24 mg/ kg RDF. Selective solvent extraction improves the reproduciblities of the technique and allows the detection of polymeric structures. Pyrograms of polyvinyl chloride and regular typing paper showed some common peaks that are present in the RDF pyrogram. About 65% of the peaks in the RDF pyrogram might be of paper origin. The organic chloride content of the RDF was evaluated by ion chromatography of the trapped pyrolyzates in 2% NaOH trap and it was found to be 221 mg Cl/ kg dry RDF. Pyrolysis conditions and temperature programs for FA were systematically evaluated. Samples included purified FA, methylated FA and HPLC separated fractions. Characteristic pyrograms were developed. Profiles of benzene, toluene, phenol, m-cresol and biphenyl from FA were evaluated. The production of phenol was the largest at 800°C, at concentration of 1.61 mg per gram of FA pyrolyzed. The profiles of benzene and toluene followed the same pathways. Both pyrolyzates had at least two precursors. HPLC fractions of FA showed some regular retention patterns characteristic of polymeric material. DL-proline, seriene and vanillic acid pyrograms showed some peaks with the same retention times as those in FA pyrogram under the same conditions. A reproducibility of 6% relative standard deviation was achieved in the pyrolysis of RDF and 0.91% in the case of FA. digital.library.unt.edu/ark:/67531/metadc331124/
Molecular Dynamics in the Liquid Phase by FT-NMR, FT-IR and Laser Raman Lineshape Analysis
Nuclear magnetic resonance (NMR) provides a convenient probe for the study of molecular reorientation in liquids because nuclear spin-lattice relaxation times are dependent upon the details of molecular motion. The combined application of Raman and Infrared (IR) lineshape analysis can furnish more complete information to characterize the anisotropic rotation of molecules. Presented here are the studies of NMR relaxation times, together with Raman/IR Mneshape analysis of the solvent and temperature dependence of rotational diffusion in 1,3,5-tribromobenzene and 1,3,5-trifluorobenzene. In these experiments, it was found that the rotational diffusion constants calculated from Perrin's stick model were two to three times smaller than the measured values of D, and D,,. Similarly, rotational diffusion constants predicted by the Hu-Zwanzig slip model were too large by a factor of 2. Application of the newer Hynes-Kapral-Weinberg model furnished rotational diffusion constants that were in reasonable agreement with the experimental results. The vibrational peak frequencies and relaxation times of the isotropic Raman spectra of the υ1 modes of CD2Br2 and CHBr3 were studied in solution. The frequency shifts in non-interactive solvents were explained well on the basis of solution variations in the dispersion energy. In Lewis bases, the displacements were in some, but not all, cases greater than predicted. On the other hand, it was found that the vibrational relaxation times of the C-H/C-D modes decreased dramatically in all Lewis base solvents. Therefore, it was concluded that relaxation times of the υ1 modes, rather than frequency shifts, furnish a more reliable measure of hydrogen bonding interactions of halomethanes in solution. digital.library.unt.edu/ark:/67531/metadc330608/
Analysis of Acid Gas Emissions in the Combustion of the Binder Enhanced d-RDF by Ion Chromatography
Waste-to-energy has become an attractive alternative to landfills. One concern in this development is the release of pollutants in the combustion process. The binder enhanced d-RDF pellets satisfy the requirements of environmental acceptance, chemical/biological stability, and being storeable. The acid gas emissions of combusting d-RDF pellets with sulfur-rich coal were analyzed by ion chromatography and decreased when d-RDF pellets were utilized. The results imply the possibility of using d-RDF pellets to substitute for sulfur-rich coal as fuel, and also substantiate the effectiveness of a binder, calcium hydroxide, in decreasing emissions of SOx. In order to perform the analysis of the combustion sample, sampling and sample pretreatment methods prior to the IC analysis and the first derivative detection mode in IC are investigated as well. At least two trapping reagents are necessary for collecting acid gases: one for hydrogen halides, and the other for NOx and SOx. Factors affecting the absorption of acid gases are studied, and the strength of an oxidizing agent is the main factor affecting the collection of NOx and SOx. The absorption preference series of acid gases are determined and the absorption models of acid gases in trapping reagents are derived from the analytical results. To prevent the back-flushing of trapping reagents between impingers when leak-checking, a design for the sampling train is suggested, which can be adopted in sample collections. Several reducing agents are studied for pretreating the sample collected in alkali-permanganate media. Besides the recommendation of the hydrogen peroxide solution in EPA method, methanol and formic acid are worth considering as alternate reducing agents in the pretreatment of alkaline-permanganate media prior to IC analysis. The first derivative conductivity detection mode is developed and used in IC system. It is efficient for the detection and quantification of overlapping peaks as well as being applicable for non-overlapping peaks. digital.library.unt.edu/ark:/67531/metadc331848/
Syntheses of Highly Strained Energetic Molecules and Development of New Synthetic Methodology
The objective of this study was to synthesize new energetic, strained, saturated polycyclic compounds. For this purpose, new methodology has been developed, as follows: (i) Ketenes have been generated in situ via treatment of aldo-, keto- or alkenoic acid with either toluenesulfonyl chloride or 2-chloro-1-methylpyridfniurn iodide (Mulkaiyama's reagent). The reactive intermediates thereby generated have been found to undergo intramolecular [2+2] cycloaddition reactions in these systems. digital.library.unt.edu/ark:/67531/metadc331132/
Synthesis and Structure of Polynitro- and Polymenthylpolycyclic "Cage" Monomers and Polymers
The objective of this study was to synthesize and characterize new energetic polycyclic "cage" compounds. As part of a program involved in the synthesis of new polynitropolycyclic compounds, 2,6-dinitro-5-methoxy- 7-carbomethoxypentacyclo[5. 3 .0 . 0* • * . CP • i ° . 0* •8]decane has been synthesized. This is a model system which can be used to study (1) the effect of nitro substitution on the photolability of carbon-carbon double bonds and (2) to develop methods for avoiding Haller-Bauer cleavage in cage /3-keto esters when synthesizing polynitro-substituted cage compounds. digital.library.unt.edu/ark:/67531/metadc332109/
The Stereochemistry of Silenes and Alpha-Lithio Silanes
When E- or Z-l-methyl-l-phenyl-2-neopentylsilene was generated by the retro-Diels-Alder vacuum-sealed tube thermolysis of its corresponding anthracene adduct, in the presence of various alkoxysilanes, only one diastereomeric adduct was formed in each case, showing that the reactions are stereospecific. An x-ray crystal structure of the methoxytriphenylsilane adduct of the E-silene confirmed its relative configuration as (R,S) or (S,R). This demonstrated that the addition of alkoxysilanes to silenes is stereospecific and syn. The relative configurations of similar alkoxysilane and alkoxystannane adducts to E- and Z-l-methyl-l-phenyl-2-neopentylsilene were assigned based on a combination of xray structures and *3C NMR data. A strong, nonbonded oxygen-metal interaction is apparent in all of those compounds studied. Treatment of the alkoxystannane adducts with alkyl lithium reagents results in tin-lithium exchange in some cases. The results indicate that the resulting <x-lithio alkoxysilanes are not configurationally stable in either THF or hydrocarbon solvents. The reaction of tert butyl lithium with a-trimethylsilylvinylmethylphenylchlorosilane in hydrocarbon solvents yields E- and Z-l-methyl-l-phenyl-2-neopentyl-2-trimethylsilylsilene. In the absence of any traps these silenes undergo a novel tert butyl lithium catalyzed rearrangement to 2-phenyl-3-trimethylsilyl-5,5-dimethyl-2-silahex-3-ene. These silenes were also trapped as their [4+2] cycloadducts with anthracene. The Z-isomer of the anthracene adduct was separated and its stereochemistry confirmed by an x-ray crystal structure. The anthracene adducts of both E- and Z-l-methyl-1-phenyl-2-neopentyl-2-trimethylsilylsilene undergo a facile, stereospecific decomposition at temperatures as low as 190°C to regenerate their respective silenes, the mildest stereospecific route to a silene yet reported. The E- and Z-silenes react stereospecifically with methanol under vacuum-sealed tube conditions. The stereochemistry of the addition is syn and a common mechanism is proposed for the addition of alcohols and the addition of alkoxysilanes to silenes. digital.library.unt.edu/ark:/67531/metadc332323/
Chromatographic and Spectroscopic Studies on Aquatic Fulvic Acid
High Performance Liquid Chromatography (HPLC) was used to investigate the utility of this technique for the analytical and preparative separation of components of aquatic fulvic acids (FA). Three modes of HPLC namely adsorption, anion exchange and reversed phase were evaluated. Aquatic fulvic acids were either extracted from surface water and sediment samples collected from the Southwest of the U.S., or were provided in a high purity form from the USGS. On the adsorption mode, a major fraction of aquatic fulvic acid was isolated on a semipreparative scale and subjected to Carbon-13 NMR and FAB Mass Spectroscopy. Results indicated that (1) The analyzed fraction of fulvic acid contains more aliphatic than aromatic moieties; (2) Methoxy, carboxylic acids, and esters are well-defined moieties of the macromolecule; (3) Phenolic components of the macromolecules were not detected in the Carbon-13 NMR spectrum possibly because of the presence of stable free radicals. Results of the anion exchange mode have shown that at least three types of acidic functionalities in aquatic fulvic acid can be separated. Results also indicated that aquatic fulvic acid can be progressively fractionated by using subsequent modes of HPLC. Results of reversed phase mode have shown that (1) The fractionation of aquatic fulvic acid by RP-HPLC is essentially controlled by the polarity and/or pH of the carrier solvent system; (2) Under different RP-HPLC conditions aquatic fulvic acid from several locations are fractionated into the same major components; (3) Fulvic acid extracted from water and sediment from the same site are more similar than those extracted from different sites; (4) Cationic and anionic ion pair reagents indicated the presence of amphoteric compounds within the polymeric structure of fulvic acid. Each mode of HPLC provided a characteristic profile of fulvic acid. The results of this research provided basic information on the behavior of aquatic fulvic acids under three modes of HPLC. Such informations are prerequisite for further investigation by spectroscopic methods. digital.library.unt.edu/ark:/67531/metadc331734/
Methods Development for Ion Chromatography
Ion chromatography (IC) as developed by Small et. al. in 1975 has become an efficient and reliable analytical technique for simultaneous analysis of multiple ions in solution. The principle requirement prior to use the IC for an analysis is sample preparation; these include sample decomposition, solvent extraction, and trapping in case the target element is in the gas phase, etc. Solvent extractions for fluoride, chloride, sodium, ammonium, and potassium ions which are soluble in soils are described. Sample decompositions include silicate rocks using hydrofluoric acid for the determination of phosphorus; organic pesticides using lithium fusion technique for the determination of halide and cyanide ions are also described. After these sample preparation techniques, the aqueous solutions obtained were analyzed on the ion chromatograph for the analyses of the anions and cations mentioned above. Recovery and reproducibility of each technique is in general quite good and the comparison between the results obtained from the IC method and other instrumentation are given. digital.library.unt.edu/ark:/67531/metadc330927/
The Nature of Intermediates Produced Through Ligand-Substitution Reactions of Octahedral Metal Carbonyls
Pulsed laser time-resolved ligand-substitution photochemistry for (DTO)W(CO)4, (DTN)W(CO)4, and (NP)Mo(CO)4 (DTO = 2,2,7,7-tetramethyl-3,6-diathiaoctane; DTN = 2,2,8,8- tetramethyl-3,7-diathianonane; NP = l-diethylamino-2- diphenylphosphinoethane) proceeds via initial fission of the W-S and Mo-P bonds, affording Cs and C4v five-coordinate intermediates for DTN and NP but largely Cs for DTO. The rates of reaction of these intermediates, via chelate ring closure and competitive bimolecular interaction with Lewis bases (= L, alkylphosphines and alkyl phosphites) for the Cs intermediates and via bimolecular interaction of L with the C4v intermediates, together with activation parameters for these processes have been determined. The rates of interactions at the Cs intermediates are significantly faster than at the C4v intermediates. digital.library.unt.edu/ark:/67531/metadc331634/
Raman and NMR Relaxation Studies of Molecular Dynamics in Liquids
Raman vibrational bands are sensitive to fluctuations in the molecular environment. Variations in the bandwidth and peak position can then be utilized to monitor molecular forces and interactions present in condense phases. Nuclear Magnetic Resonance (NMR) provides a convenient probe for the study of molecular reorientation in liquids since nuclear spin relaxation times are dependent on the details of molecular motion. Presented here is the solvent study of the Raman bandwidths and frequency displacements of the mode of the compounds CH3MCI3 (M = C, Si, Ge, Sn) in a number of solvents of widely varying molecular structure. Also, a detailed isotope dilution study of the modes in CH2CI2/CD2CI2 mixtures is presented. In this set of experiments, I observed broadening of the v1 mode of CH2C12 upon dilution,which is the first experimental observation of such behavior. The temperature-dependent carbon-13 relaxation times and nuclear Overhauser enhancements in neat dichloromethane were measured. In this study we found that the molecular reorientation of this molecule was highly anisotropic, but could be well characterized assuming quasi-symmetric top behavior. In addition, in order to gain a more complete understanding of the reorientational dynamics in dichloromethane, we analyzed the 13-C NMR relaxation of CH2CI2 both in "inert" solvents of differing viscosities and in interactive solvents of varying Lewis basicities. Various theoretical models were also applied in order to characterize dichloromethane1s reorientational dynamics. digital.library.unt.edu/ark:/67531/metadc330818/
Intramolecular 2+2 Cycloadditions of Ketenes
The objective of this study was to explore intramolecular ketene cycloadditions with the anticipated results of developing new synthetic methodology for the synthesis of polycyclic compounds difficult to obtain by other procedures. (o-Alkenylphenoxy)ketenes were initially selected for this study because these ketenes provided a favorable proximity for the intramolecular [2+2] cycloaddition reactions. The difunctional precursors, (o-alkenylphenoxy)- acetic acids, were readily prepared from o-alkenylphenols and ∝-halocarboxylic acids and were converted to the corresponding acid chlorides by reaction with oxalyl chloride. The acid chlorides were dehydrochlorinated to the corresponding (o-alkenylphenoxy)ketenes by treatment with triethylamine. The ketenes undergo a facile intramolecular [2+2] cycloaddition to give polycyclic eye 1obutanones. The (o-vinylphenoxy)ketenes are clearly more reactive than the (o-allylphenoxy)ketenes and provide much better yields of the cycloaddition products because of electronic effects in the transition state in the cycloaddition process. The intramolecular [2+2] cycloadditions of keteniminium salts were included in this study as a more electrophilic alternative to ketenes that will react with less nucleophilic carbon-carbon double bonds. However, the use of keteniminium salts instead of ketenes in Intramolecular cycloadditions does have some limitations. The synthesis of benzofurans via the intramolecular [2+2] cycloadditions of (o-acylphenoxy)ketenes was accomplished. The initially formed ß-lactone cycloaddition products spontaneously underwent decarboxylation to the benzofurans. The aromaticity of the benzofurans is apparently a very strong driving force for the cycloaddition. During the course of this study, two new synthetic methods were discovered which in many instances represent a significant Improvement over existing methods. The Wittig Reactions of ketoacids without protecting the carboxyl groups provide a reliable source of the precursor unsaturated acids needed for intramolecular ketene-olefin cycloadditions. Also, the one-pot preparation of intramolecular ketene cycloaddition products from the carboxylic acid via the tosylate represents a new synthetic method. This procedure eliminates the acid halide preparation, isolation and purification step, thereby significantly simplifying the synthesis. digital.library.unt.edu/ark:/67531/metadc331159/
Silenes and Silenoids in the Chemistry of Cyclopentadienylsilanes
Evidence is presented that apparent silene products obtained from the metalation of cyclopentadienyldimethyl - chlorosilane either with tert-butyl1ithium or with methylenetriphenylphosphorane actually arise from the metalated starting material, a silenoid, rather than from a silafulvene intermediate. Trimethylmethoxysi1ane is shown to be an effective trap for dimethylsilafulvene. A new dimethylsilafulvene precursor, bis(dimethylmethoxysi1yl) cyclopentadiene, which gives high yields of dimethyldimethoxysi1ane and the silafulvene at temperatures as low as 240°C is reported. digital.library.unt.edu/ark:/67531/metadc331302/
Stoichiometry and Deposition Temperature Dependence of the Microstructural and Electrical Properties of Barium Strontium Titanate Thin Films
Barium Strontium Titanate (BST) was deposited on Pt/ZrO2 / SiO2/Si substrates using liquid source metal organic chemical vapor deposition. A stoichiometry series was deposited with various GrII/Ti ratios (0.658 to 1.022) and a temperature series was deposited at 550 to 700°C. The thin films were characterized using transmission electron microscopy. Both series of samples contained cubic perovskite BST and an amorphous phase. The grain size increased and the volume fraction of amorphous phase decreased with increasing deposition temperature. The electrical and microstructural properties improved as the GrII/Ti ratio approached 1 and deteriorated beyond 1. This research demonstrates that BST thin films are a strong candidate for future MOS transistor gate insulator applications. digital.library.unt.edu/ark:/67531/metadc279410/
Synthesis, structure and redox reactivity of Co₃(CO)₆(μ₂-η²,η¹-C(Ph)C=C(PPH₂)C(O)SC(O)) (μ₂-PPh₂)
The tricobalt cluster PhCCo₃(CO)₉ (1) reacts with the bidentate phosphine ligand 2,3-bis(diphenylphosphino)maleic thioanhydride (bta) with added Me₃NO to yield PhCCo₃(CO)₇(bta) (2), which upon heating overnight yields Co₃(CO)₆(μ₂-η²,η¹-C(Ph)C=C(PPH₂)C(O)SC(O)) (μ₂-PPh₂) (3). Cluster (3) has been isolated and characterized by FT-IR and ³¹P NMR spectroscopy. Structural determination of the cluster has been demonstrated by X-ray diffraction analysis. Cluster (3) is analogous to the cluster synthesized by Richmond and coworkers. The redox properties of (3) have been examined by cyclic voltammetry and the data are reported within. digital.library.unt.edu/ark:/67531/metadc279408/
Survey of the Solid State Conformation of Calix[4]arenes
The characteristics of seventy-six calix[4]arene crystal structures derived from the Cambridge Crystallographic Database are presented. This survey is a discussion of the inter and intramolecular effects on the solid state cavity shape and molecular recognition ability of the compounds. In addition to this survey, four new calix[4]arene crystal structures are presented. The conformational characteristics of these four calixarenes are determined by a complicated array of inter and intramolecular interactions in the crystal packing. digital.library.unt.edu/ark:/67531/metadc278942/
Interactions of Clean and Sulfur-modified Reactive Metal Surfaces with Aqueous Vapor and Liquid Environments : A Combined Ultra-high Vacuum/electrochemistry Study
The focus of this research is to explore the molecular-level interactions between reactive metal surfaces and aqueous environments by combined ultra-high vacuum/electrochemistry (UHV-EC) methodology. The objectives of this work are to understand (1) the effects of sulfate ions on the passivity of metal oxide/hydroxide surface layer, (2) the effects of sulfur-modification on the evolution of metal oxide/hydroxide surface layer, and (3) the effects of sulfur adsorbate on cation adsorption at metal surfaces. digital.library.unt.edu/ark:/67531/metadc278914/
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. digital.library.unt.edu/ark:/67531/metadc278936/
Mobile Order Theory as Applied to Polycyclic Aromatic Heterocycles
Experimental mole fraction solubilities of benzil, thianthrene, trans-stilbene, thioxanthen-9-one, diphenyl sulfone and dibenzothiophene sulfone are determined in pure noncomplexing and complexing solvents. Predicted solubility values are calculated for benzil, thianthrene, trans-stilbene and thioxanthen-9-one using expressions derived from Mobile Order theory. Large deviations between experimental and predicted solubilities in alcohol solvents exist, therefore optimized solute - solvent association constants are determined. Previously measured thianthrene solubilities in five binary alkane + cyclohexane solvent mixtures are compared with values predicted from Mobile Order theory using the measured solubility in each of the pure solvents as input parameters. The experimental mole fraction solubility of benzil in eight binary alcohol + 1-octanol solvent mixtures are also measured and compared with predicted values. digital.library.unt.edu/ark:/67531/metadc278994/
Kinetics and Mechanisms of Metal Carbonyls
Pulsed laser flash photolysis with both visible and infrared detection has been applied to the study of the displacement of weakly coordinating ligands (Lw) by strongly "trapping" nucleophiles (Ls) containing either an olefinic functionality (Ls = 1-hexene, 1-decene, 1-tetradecene) or nitrogen (Ls = acetonitrile, hydrocinnamonitrile) from the photogenerated 16 electron pentacarbonylchromium (0) intermediate. 5-Chloropent-l-ene (Cl-ol), a potentially bidentate ligand, has been shown to form (ol-Cl) pentacarbonylchromium (0), in which Cl-ol is bonded to Cr via a lone pair on the chlorine, and isomerize to (Cl-ol) pentacarbonylchromium (0), in which Cl-ol is bonded to the olefinic functionality on the submillisecond time scale. This process has been studied in both the infrared and visible region employing both fluorobenzene or n-heptane as the "inert" diluent. Parallel studies employing 1-chlorobutane and 1-hexene were also evaluated and showed great similiarity with the Cl-ol system. The data supported a largely dissociative process with a possibility of a small interchange process involving the H's on the alkyl chain. Studies were also carried out for various Cr(CO)6/arene/Ls systems (arene = various alkyl or halogenated substituted benzenes). The data indicated that for both C6H5R (R=various alkyl chains) or multi-alkyl substituted arenes (i.e. o-xylene, 1,2,3-trimethylbenzene) containing an "unhindered" ring-edge, bonding to the the Cr(CO)5 moiety occurs "edge on" via a partially delocalized center of unsaturation on the ring. The data indicated that both electronic and steric properties of the arenes influence the kinetics, and that an interchange pathway takes place at least, in part, through the alkyl chains on both the arenes and "trapping" nucleophiles. Moreover, halogenated arenes bond through the lone pair on the halogen for both CI- and Br- derivatives but "edge-on" for the fluorinated arenes. Finally, in the case of arene complexes without and "unhindered" ring-edge (i.e., 1,2,3,4,5-pentamethylbenzene) bonding can occur either "edge-on" or through the ring center of the arene or combination of the two. Carbonyl stretching frequencies for the arenes are also indicative of the type of bonding. digital.library.unt.edu/ark:/67531/metadc278709/
Syntheses of Antimetabolites
In these studies several different types of antimetabolites were synthesized, and their biological effects were examined in various assay systems. More extensive investigations were done in microbial systems in which many of the compounds proved to be inhibitory to growth, and attempts were made to determine the mode of biochemical action by adding supplements of the appropriate natural metabolite. digital.library.unt.edu/ark:/67531/metadc279358/
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