Chemistry & Biochemistry Theses and Dissertations
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Item Experimental and Theoretical Characterization of Effective Interactions Near 132Sn(1987) Stone, Craig A.; Walters, William B.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)Experimental investigations have been undertaken to study the multiplet structure in six nuclei near 132Sn: 132,130Sb, 131,129,127Sb, and 132Te. Experiments were performed using ion beams of mass-separated fission products produced by the TRISTAN mass separator at Brookhaven National Laboratory. Extensive four-detector gamma-gamma coincidences, gamma-multiscaling and conversion-electron data have been collected. Ultralarge shell model calculations were performed using the VLADIMIR shell model code on the Cray/CDC 7600 supercomputer system at Lawrence Livermore National Laboratory. These calculations were designed to look at the performance of the Kallio-Kolltveit and Siemen's g-matiix potentials on the 1-3 quasiparticle nuclides in the gddsh model space. Results show that realistic potentials work well on nuclei near 132Sn but show problems with 129,130Sn and 131Sb which can not be accounted for by core-polarization corrections. Problems are shown to be due to the use of a potential derived with the Scott-Moszkowski separation metl1od. The separation distance was demonstrated to have a weak dependence on the principal quantum number but a strong dependence on the orbital angular momentum. This suggests the Kallio-Kolltveit potential is underestimating the strength of the h11/2 interactions in 129,130Sn and 131Sb.Item Spacial and Temporal Variations in 36CI Deposition in the Northern United States(1994) Hainsworth, Laura J.; Mignerey, Alice C.; Chemistry and Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Chlorine-36, a cosmogenic radioisotope, has been developed for use as a tracer in hydrological systems. The deposition of atmospheric 36Cl, although of primary importance to hydrological applications, has not been well studied. To begin to address this problem, 36Cl has been measured in monthly, wet-only, precipitation samples collected from February, 1991, to January, 1993, at the Elms Environmental Education Center in St. Mary's County, Maryland. In addition, bulk deposition samples were collected over a 1 y period at seven sites across the Northern United States and analyzed for 36CI. The mean, wet-only 36Cl/Cl ratio for the 2 y sampling period is 68±19 (x10 -15), and the mean 36 CI concentration is 1.2±0. 1 (x10 6) atoms/L. The 36Cl wet deposition flux data reveal a distinct seasonal deposition pattern, with peaks occurring in March and April. This pattern is attributed to stratospheric/ tropospheric exchange. The mean 36Cl wet deposition flux is 38.2±5 atoms/m2s. Comparison between wet-only and bulk deposition samples indicates that the difference accounts for approximately 25% of the total 36Cl deposition flux at the Elms site. A new model, using 90Sr to predict the 36CI deposition pattern, is developed to predict 36Cl/Cl ratios across the United States. Chlorine-36/Cl ratios in bulk deposition samples collected across the northern United States agree well with the model predictions. A mean global 36Cl production rate of approximately 28 to 38 atoms/m2s is indicated by these samples. A comparison between 36Cl concentrations in the Aquia and Magothy aquifers is southern Maryland and bulk deposition samples collected at the Elms, MD, site indicated that modern precipitation can account for the 36Cl content in the youngest water in these aquifers. Surface water samples from the Susquehanna River basin reveal 36 Cl and stable chloride concentrations an order of magnitude higher than in bulk deposition samples collected at State College, PA. The source of excess 36Cl in the Susquehanna is not known. Possible explanations include 'bomb-pulse' 36Cl and in-situ 36CI production in surface rocks.Item The Photochemistry of Amides and Phthalimides(1977) Bowen, Michael William; Mazzocchi, Paul H.; Organic Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md); ILLiad # 1481769N-Alkyl amides undergo photodecomposition much slower than their ketone, ester, and aldehyde analogs . The Norrish Type II process in amides is also less important than in these other classes of compounds due to electronic and geometric effects. Type II products account for less than 10% of the decomposed amides in all cases and usually less than 5%. A 2% solution of amide in dioxane, when irradiated through quartz with light >200 nm, did not decompose in the Type II fashion to yield N-alkyl acetamides, alkenes, and unsubstituted amides. The preferred reaction mode was the Norrish Type I process where the O=C+N bond or the O=C+C bond was cleaved to yield either an acyl radical and amine radical or an acyl radical and alkyl radical. These photochemically unstable radicals, once produced, rapidly underwent secondary reactions to yield smaller molecules. These molecules were detected, underwent further reactions (polymerization; photoreduction), or interacted with the solvent . The dimers of dioxane and cyclohexane, created via hydrogen abstraction, were the main products of amide photodecomposition in these solvents. Small aldehydes and alkenes produced as intermediates, underwent inefficient photoreductions with solvent to afford alkyl dioxanes and cyclohexanes and the two diastereomers of ( 2-p-dioxyl ) ethanol as other major products. The alcohols were also produced by photoreduction of acetaldehyde and hexanal as well as by direct photodecomposition of dioxane . Tertiary amides reacted faster than secondary amides. The Type I reaction was accelerated by electronic (inductive) factors. The Type II reaction was also more efficient due to geometric and electronic factors. The Type I amine product, dihexylamine, was observed as an intermediate in the photodecomposition of N, N-dihexylhexanoamide . Unsymmetrical anilide imides photodecomposed in dioxane to yield a wide variety of products. The Photo-Fries decomposition mode was most favored where acyl groups migrated to positions ortho and para to the amine substituent. For example, N-acetyl-butyranilide decomposed to yield o- and p-acetoaniline, o - and p-butyraniline , o- and p-acetobutyranilide, and o- and p-butyracetanilide. Very little Type II decomposition was observed, that is, N-acetyl-butyranilide yielding N, N -diacetylaniline or o- and p-acetoacetanilide. N-Alkylphthalimides were the sole group of amides or imides reported in the literature to undergo efficient Y-hydrogen abstraction. These compounds underwent initial Y-hydrogen abstraction to yield a 1,4-biradical followed by ring closure to form an azacyclobutanol intermediate. The intermediate then underwent retrotransannular ring opening to yield various 3,4-benzo-6,7-dihydro(1H)azepine-2,5-diones. Dihydrophthalimide alkenes were minor products in acetonitrile which arose after the initial y-hydrogen abstraction via subsequent δ-hydrogen transfer. Quantum yield determination as well as mechanistic investigation was conducted . The quantum yields varied from 0.023 to 0.003. Photolysis of an optically active phthalimide with an asymmetric Y-position to yield starting material of the same activity proved that the initial hydrogen abstraction was irreversible. A Type I cleavage to yield phthalic anhydride on treatment with silica gel and heat was important when they Y-position was tertiary. A quenching study of these N-alkylphthalimides with piperylene showed acceleration of starting material disappearance but decrease in product formation. An additional reaction process was interfering with the azepinedione formation. Liquid chromatography showed formation of several highly alkylated products which could not be isolated in pure form. N-Methylphthalimide, which could not ring expand, was irradiated with various alkenes to produce analogous N-methylazepinediones. The mechanism involved a 2 + 2 cyclo-addition of the double bond to the C-N bond to yield a dipolar azacyclobutanc intermediate. The intermediate with a retrotransannular ring opening yielded the observed 3, 4- benzo-6,7-dihydro-1-methylazepine-2,5-diones. These reactions prove that the C-N bond in phthalimide is of a substantial double bond character.Item Investigation of the Tetrahymena Pyriformis 2-Aminoethylphosphonic Acid Biosynthetic Pathway and the P-C Bond Forming Enzyme Phosphoenolpyruvate Mutase(1991) McQueney, Michael Scott; Dunaway-Mariano, Debra; Chemistry and Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The biosynthetic pathway leading to 2-aminoethylphosphonate in Tetrahymena pyriformis was determined. A cell-free homogenate of T. pyriformis converted phosphoenolpyruvate to AEP in 37% yield, phosphonopyruvate to AEP in a 11 % yield and phophonoacetaldehyde to AEP in an 83% yield. The Tetrahymena pyriformis enzyme, PEP mutase was purified. The PEP Mutase catalyzes the rearrangement of phosphoenolpyruvate to phosphonopyruvate and the equilibrium constant is >500:1 in favor of phosphoenolpyruvate. To distinguish between an intra-and intermolecular reaction pathway for this process an equimolar mixture of [P= ^18O, C(2)- ^18 O]thiophosphonopyruvate and (all - ^16Q)thiophosphonopyruvate was reacted with the PEP mutase and the resulting products were analyzed by ^31P-NMR. The absence of the cross over product [C(2)-18O]thiophosphonoenolpyruvate in the product mixture was interpreted as evidence for an intramolecular reaction pathway. To distinguish between a concerted and stepwise intramolecular reaction pathway the pure enantiomers of the chiral substrate [P= ^18Q]thiophosphonopyruvate were prepared and the stereochemical course of their conversion to chiral [P= ^18O]thiophosphoenolpyruvate was determined. Based on the observed conversion of (Sp) - [P= ^18O]thiophosphonopyruvate to (Sp)-[P= ^18O]thiophosphoenolpyruvate and (Rp) - [P = ^18O]thiophosphonopyruvate to (Rp)[P= ^18O]thiophosphoenolpyruvate it was concluded that the PEP phosphomutase reaction proceeds with retention of the phosphorus configuration and therefore by a stepwise mechanism. The similar reactivity of the oxo and thio substituted phosphonopyruvate substrates (i.e., nearly equal Vmax) was interpreted to suggest that addition to the phosphorus atom is not rate limiting among the reaction steps. Lastly, single turnover experiments failed to trap a pyruvate in the PEP mutase reaction.Item The Role of Hydrogen Cyanide in Chemical Evolution(1989) Navarro-González, Rafael; Ponnamperuma, Cyril; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Two major research areas are investigated: The electrosynthesis of hydrogen cyanide; and the role of cyanocomplexes in the free - radical oligomerization of hydrogen cyanide. The electric discharge production of hydrogen cyanide from a simulated primitive atmosphere composed of methane, nitrogen and water vapor was investigated. The radiation chemical yield (G) of formation of HCN was determined to be 0.26. A free radical mechanism was proposed to account for the observed chemical changes. Computer simulations of the reaction mechanism could effectively model the early stages of electrolysis of the gas mixture, and permitted the estimation of the rate of electrosynthesis of hydrogen cyanide under various atmospheric conditions . The possible role of cyanocomplexes of transition elements on the free- radical oligomerization of hydrogen cyanide was investigated. Aqueous, oxygenfree, dilute solutions of hydrogen cyanide and hexacyanoferrate(II) or (III) were submitted to various doses of gamma irradiation. The presence of either cyanocomplex led to a significant decrease in the rate of decomposition of hydrogen cyanide. The major products were ammonia and carbon dioxide . Computer simulations of these systems permitted the elucidation of the reaction mechanism and the derivation of rates of reactions of free- radicals with the cyanocomplexes. The results obtained provide an insight into the possible role of cyanocomplexes of transition elements in chemical evolution.Item Heats of Combustion and Formation of Some Simple Aliphatic Amines(1958) Jaffe, Irving; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)Item CHROMIUM OXIDATION AND REDUCTION BY HYDROGEN PEROXIDE IN DIVERSE SOILS AND SIMPLE AQUEOUS SYSTEMS(1999) Rock, Melanie Louise; Helz, George R.; James, Bruce R.; Chemistry; Environmental Science & Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Hydrogen peroxide is being tested for in situ remediation of buried contaminants - either as a direct chemical oxidant in Fenton-type reactions or as a source of oxidizing equivalents in bioremediation. How it affects a common co-contaminant, Cr, is explored here in four chemically diverse high-Cr soils. Soils contaminated with high levels of soluble Cr(VI) from ore processing and soils containing high levels of recently reduced Cr(III) from electroplating waste showed marked increases in chromate after single applications of J-25 mM peroxide. Cr(VI) in the leachates exceeded the drinking water standard (2μM) by 1-3 orders of magnitude. Soluble Cr(III), in the form of dissolved organic complexes, contributed to the likelihood of Cr(III) oxidation. Anaerobic soil conditions at a tannery site prevented oxidation of Cr(III). Naturally occurring Cr in serpentine soil also resisted oxidation. Ambient soluble Cr(VI) in a contaminated aquifer disappeared from peroxide leachates below pH 5, then reappeared as peroxide levels declined. In solutions prepared under environmentally relevant conditions, aged 280 μM Cr(III) treated with 100 μM H2O2 showed increases in Cr(VI) over weeks with maximum oxidation rates achieved in solutions prepared with 2:1 and 4:1 OH^-:Cr. Although Cr(III) speciation differs in fresh and aged aqueous systems, a similar mechanism involving the pre-equilibrium step: Cr(OH)/ + OH- .,. Cr(OH)/ may account for Cr(III) oxidation in both systems. Under alkaline conditions, H2O2 enhanced the oxidative dissolution of Crn(OH)3n^0. The formation of peroxochromium compounds in the presence of H2O2 and Cr(VI) may account for the disappearance and reappearance of Cr(VI) in H2O2 treated soils; as does the possible formation and subsequent reoxidation of Crm\(OH)3n-2^2+ oligomers. Mobilization of hazardous Cr(VI) must be considered in plans to use H2O2 for remediation of chemically complex wastes. Once Cr(III) is oxidized to Cr(VI) by H2O2 it may persist long after applied H2O2 treatments have disappeared. Further, hexavalent Cr will behave as a catalyst toward H20 2 in soils, enhancing its oxidative capacity while helping to dissipate high levels of applied H2O2.Item The Effect of Changes in Structure of the Reactants on the Rate of Enamine Formation(1964) Marchese, James Salvatore; Pratt, Ernest F.; Chemistry & Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)It has been found that the rate of formation of a wide variety of enamines can be accurately determined by observing the rate at which the by-product water collects in a Dean-Stark trap. On the basis of the results observed upon varing the reactant ratio, the catalyst concentration and the temperature, 0.125 mole of carbonyl compound, 0.375 mole of amine and .001 mole of p-toluenesulfonic acid dissolved in sufficient benzene to give a total volume of 500 ml. were employed in the standard procedure. The solution of reactants was heated under reflux in an apparatus fitted with a water trap and frequent readings of time and water volume were taken until the reaction was complete. Nearly quantitative (98 to 100%) yields of water were ordinarily obtained and 85 to 100% yields of enamine were usually isolated. As the structure of the carbonyl component was varied an extremely wide range of reaction rates was encountered. The relative reactivity of many of these compounds had not been determined preciously. It was found that the rate decreased markedly among cyclic ketones as the ring was expanded from five to six to seven members and also when the methyl group of methylcylohexanones were shifted from the four to the three to the two position, Steric effects appear to be responsible for these rate differences. Somewhat unexpectedly ∝-tetralone did not react while β-tetralone reacted smoothly. Although the literature contains very little information on the formation of enamines of diketones a number of these were converted to the mono-enamines very smoothly. The rate decreased in the sequence, 1, 3-cyclohexanedione, dimedone, acetylacetone, benzoylacetone and 2-acetylcyclopentanone. Some evidence that ketones having planar structures reacted faster than those with non-planar structures was found, but no obvious correlation between degree of enolization and rate of reaction was observed. The reaction of acetophenones was much improved when the reaction temperature was changed from 82° to 112° by using toluene as a solvent. As the electron attracting ability of the para substitute was inreased in the order, CH3, H, Cl and N02 the rate consistently increased. Phenylacetone reacted smoothly under the standard conditions, but heptanone-2 gave only a 27% yield of water in five days . The importance of steric factors is emphasized by the fact that cyclohexanone gave a 98% yield of water in two hours. Typical aliphatic aldehydes reacted so rapidly that in order to increase the accuracy of t;he rate measurements 0.000125 mole of catalyst was used in place of the standard 0.001 mole. The order of decreasing rate was phenylacetaldehyde, It is apparent that the rate decreasing effect of chain branching at the alpha position diminishes when the branches are joined into a ring. The results for phenylacetaldehyde and phenylacetone indicated that aldehydes react over one thousand times as fast as ketones. The rate of formation of enamines from cyclohexanone and a variety of amines was also determined under the standard conditions. Shifting a methyl group on the piperidine ring from the four to the three to the two position greatly decreased the rate and pyrrolidine reacted faster than both piperidine the and hexamethylene imine. Morpholine and especially N methylpiperazine reacted much faster than piperidine while n-butylmethylamine reacted most slowly of all the amines mentioned. In only a few special cases was integral order kinetics obtained. The results can, however, be quite well correlated with a straightforward mechanism if it is assumed that both the step in which the amine adds to the carbonyl group and the step in which this addition product is dehydrated ordinarily affect the overall rate.Item Micro-scale Chemical Effects of Low Temperature Weathering of DSDP Basaltic Glasses(1979) Ailin-Pyzik, Iris Blanche; Sommer, Sheldon E.; Chemistry & Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Unaltered deep-sea basaltic g lasses are believed to be the best record of initial magma composition , and as such are important in the study of petrogenesis. However , these glasses are altered by their long contact with seawater, becoming hydrated and undergoing chemical exchange. This chemical exchange affects the composition of seawater and plays a role in the chemical equilibrium of t he oceans. A study of the trace metal and major element alteration of glasses from Deep Sea Drilling Project Site 396B has been conducted, using a selected area x - ray fluorescence technique (developed for this study) for the trace metal analyses, and the electron rnicroprobe for the major elements. The samples included sections of pillow basalt rinds, hyaloclastite s, and a few crystalline sections. The glasses were found to release a bout o ne- half the original Si and Al, two- thirds of the Mg and Na , and over 90% of the Ca originally present, during alteration to palagonite. Fe and Ti were found to be immobile, and K was increased 40-fold by concentration from seawater. For the trace metals, over one-quarter of the Zn, Cu and Ni were released, 40% of the Mn, and over 10% of the Cr. These changes apply only to the conversion of fresh glass (sideromelane ) to palagonite (smectite), and do not include the effects of authigenic phillipsite and calcite reprecipitated locally. Differences between the effects of low temperature weathering on the crystalline basalts and the glasses appear to be primarily a function of the susceptibility of the primary mineral phases to attack, with the glass, being the least stable phase, being the most altered.Item Transition Metal Polypnictides from Zintl Ions(1995) Charles, Scott; Eichhorn, Bryan W.; Chemistry & Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The chemistry of the soluble E7 3- ions (E = P, As, Sb) with various transition metal complexes has been investigated. Alloys of K3E7 react with (arene)M(CO)3 (M = Cr, Mo, W) complexes in the presence of three equivalents of 2,2,2-crypt in ethylenediamine to give [K(2,2,2-crypt)]3[E7M(CO)3] complexes. Nine [E7M(CO)3] 3- compounds (E = P, As, Sb; M = Cr, Mo, W) have been prepared. The compounds have norbomadiene-like E7 fragments, with a formal negative charge associated with the unique two-coordinate pnictogen furthest from the transition metal. The bonding is described as E7 π-type interactions with the metal center. 31p NMR studies show that these compounds undergo an intramolecular wagging process in solution. The [E7M(C0)3] 3- ions are modestly basic and highly nucleophilic. The complexes react with weak acids, tetraalkylammonium salts and (arene)M'(CO)3 complexes to form the [K(2,2,2-crypt)]2[HE7M(CO)3], [K(2,2,2- crypt)]2[RE7M(CO)3] and [K(2,2,2-crypt)]3[(L2)(CO)3M'E7M(CO)3] compounds, respectively. Each of the structures contains a norbornadiene-like E7 fragment bound η4 to the M(CO)3 fragment and η1 to the appended moiety [H+, R+, M(CO)3(en)] that is attached to the pnictogen atom furthest from the M(CO)3 center. The [K(2,2,2-crypt)]3 [η4-E7M(CO)3] complexes also react with carbon monoxide at the M(CO)3 center and reversible binds CO to form [K(2,2,2-crypt)]3[η4-E7M(CO)4] complexes. These complexes are more easily protonated and undergo faster alkylations of the E7 cages than the parent [K(2,2,2-crypt)]3[η4-E7M(CO)3] compounds. Each of these structures contains an E7 fragment bound η2 to the M(C0)4 center. Products were characterized by various physical and spectroscopic techniques including UV-vis, IR, 1H, 13C, and 31P NMR spectroscopies, mass spectrometry, elemental analyses, and single crystal X-ray diffraction studies.