<p> A 19F nmr study has shown that SeO2F2, SeOF2 and SeOCl2 behave as bases (B) towards SbF5 forming the adducts, (SbF5)n•B where n = 1-5 and in which they are bonded to antimony through an oxygen. Structural information about these adducts was also obtained. Solutions of SbF5 in SeOF2 and SeOCl2 were also shown to contain the SbF-6 and cis and trans [SbF4 (B)2]+ ions. The order of basicity towards SbF5 for the following bases is, SeOCl2 > SeOF2 > SbF-6 > SOF2 > SeO2F2 > SO2ClF.</p> <p> A 77Se nmr study of the SeOCl2 solvent system has shown that the order of Lewis acidity for the following acids is, SbF5 ~ SO3 > SbCl5 > SnCl4 > SbCl3 > AsCl3.</p> <p> A new selenium oxyfluoride, SeOF4 has been identified and is shown to form an ionic adduct SeOF+3SbF-6 with SbF5.</p> <p> Polyselenium oxyfluorides, F(SeO3)nSeO2F, where n=1-3, were prepared and are found to have acyclic structures. The 77Se spectra of Se4^2+ and Se8^2+ were studied. </p> <p> Redistribution reactions between selenium and phosphorus halides and oxyhalides were studied using the nmr resonances of 19F, 31P and 77Se.</p> / Thesis / Doctor of Philosophy (PhD)

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Road construction through sulfidic materials in Virginia has resulted in localized acid rock drainage (ARD) that threatens water quality, fill stability, integrity of building materials, and vegetation management. The objectives of this study were: i) to develop a state-wide sulfide hazard rating map based on characterization of the geologic formations associated with acid roadcuts, ii) to estimate depth to sulfidic sediments in the Coastal Plain based on landscape relationships, and iii) to evaluate potential acidity testing procedures on diverse materials. Geologic formations associated with acid roadcuts were characterized by potential peroxide acidity (PPA) and S content, and grouped into four categories. Listed in order of increasing severity, these formations included: the Tabb Formation (Coastal Plain), the Lynchburg Group of the Ashe Formation (Blue Ridge), the Chesapeake Group and Lower Tertiary deposits (Coastal Plain), the Millboro shale, Marcellus shale, Chatanooga shale and Needmore Formation (Valley and Ridge), and the Quantico Formation (Piedmont). Evaluation of landscape parameters near Richmond, Virginia, indicated that the likelihood of encountering sulfidic materials within a given depth at a specific location was related to elevation and mapped soil types. Elevation and soil map units were assigned to risk classes to indicate the likelihood of encountering sulfides within a depth of 9 m. Comparison of PPA and S content for 296 diverse samples indicated that S may serve as a screening tool to evaluate materials without carbonates. Comparison of PPA and conventional Acid-Base Accounting (ABA) for 14 diverse samples indicated that PPA and ABA were highly correlated, with PPA yielding 0.60 to 0.95X the amount of acidity as ABA. Potential acidity by Soxhlet extraction and PPA were equivalent for 3 of 4 diverse samples. Average acidity and metal contents of leachate from Soxhlet extractors were correlated with acidity and metals of road drainage. Sulfide hazard analysis should be an essential step in the pre-design phase of highway construction and other earth-disturbing activities. / Ph. D.

Soil acidity is a major cause of low yields of alfalfa (Medicago sativa L.) in the southeastern United States. Two field experiments were conducted on an Ernest silt loam soil (fine—loamy, mixed, mesic Aquic Fragiudult) to determine what conditions are necessary for optimal alfalfa growth in an acid soil environment. In the first experiment alfalfa was no—till planted to evaluate the influence of surface applied dolomitic limestone at 0 and 6.7 Mg/ha either 8 or 20 months before planting and at planting on alfalfa performance under acidic conditions. Yield increases, greater than two fold, resulted from surface application of limestone regardless of time of application. In the second field experiment treatments included surface and incorporated dolomitic limestone at either 6.5 or 13.0 Mg/ha, gypsum at 13.0 Mg/ha, foliar Mo at 560 g/ha and N as a split. Yields increased in response to surface and incorporated lime, Ca, Mo and N application, possibly as a result of Al activities in soil solution being as low as 0 and 0.05 uM in the surface and 1 m depth samples, respectively, for the surface limed soils. Low activity of Al in soil solution may explain why subsurface acidity was not toxic to alfalfa grown on these soils. This study showed that surface limestone at half the recommended rate is adequate for the growth of alfalfa under acidic conditions. The implanted soil mass technique was used to evaluate the influence of subsurface amendments (Ca, N, Ca and N, KOH and Ca(OH)2) on alfalfa root growth and N fixation on soils that received either 0 or 6.7 Mg/ha surface applied limestone. Of the various subsurface amendments the Ca(OH)2 treatment produced the most root growth and N fixation. This study showed that both the reduction in acidity and the availability of Ca are necessary for optimal N fixation and root growth. In vitro studies conducted in growth pouches showed that pH 4.5 nutrient solution was not ·detrimental to alfalfa growth unless A1 was present. Addition of 3.0 mM Ca to a nutrient solution containing 0.08 mM Al alleviated toxic effects of Al on alfalfa growth. No-till alfalfa can thus be grown on acid soils with surface lime by providing Ca and reducing acidity. / Ph. D. / incomplete_metadata

The biodegradation potential of two subsurface soils was characterized by monitoring the biodegradation of short-chain fatty acids in anaerobic soil microcosms. Valerate, butyrate, propionate, and acetate concentrations were monitored independently using separate microcosms. The effect of sulfate on the microbial communities was also investigated. One soil, from Newport News, Virginia, consisted of a sandy loam collected beneath a low lying, grassy field. The microcosms containing the soil were characterized by: a neutral pH, the utilization of sulfate with concomitant precipitation of iron sulfide , an increase in the degradation rate as a result of sulfate addition, and a production of bicarbonate directly related to acid mineralization. Another soil, from Blacksburg, Virginia, consisted of a silty-clay collected beneath a wooded hilltop. Microcosms containing the soil were characterized by : a pH between 4 and 5, little sulfate utilization with no visible iron sulfide precipitation, an increase in degradation rates upon the addition of sulfate, and little or no accumulation of bicarbonate. These results indicate that short-chain fatty acids are readily degraded in subsurface anaerobic soil systems and that these rates are dependent on the availability of electron acceptors and the diversity of the indigenous population. / Master of Science

The compounds 12-phenoxy-dodecane-1-thiol, 4-dodecyloxymercaptophenol and 3-dodecyloxymercaptophenol have been synthesized using a novel synthesis to investigate the effect that the orientation of the functional group has on surface acidity. 3-dodeycloxymercaptophenol and 4-dodecyloxymercaptophenol differ in that the hydroxyl group is substituted on different carbons of the benzene ring. The difference in substitution patterns should present the hydroxyl group in different orientations in the interface between a self-assembled monolayer of the compound and aqueous solutions buffered over a pH range of 3-13. By preparing self-assembled monolayers of these molecules on gold substrates, the ability of the hydroxyl group to donate its proton was shown to depend on the hydroxyl group substitution pattern on the benzene ring through contact angle titration experiments. 3-dodecyloxymercaptophenol clearly showed plateaus at low and high pH with a broad transition between the two plateaus. 4-dodecyloxymercaptophenol showed a clear plateau at low pH but not at high pH, although a transition was observed. Using infrared spectroscopy, it was further shown that the long molecular axis of the benzene ring in 3-dodecyloxymercaptophenol was tilted from the surface normal by 55&#176;. The short molecular axis of the ring was twisted out of the plane of the surface by 28&#176; for self-assembled monolayers of this molecule on gold substrates. In contrast, the tilt angle of 4-dodecyloxymercatophenol was measured to be 46&#176; and was twisted out of the surface plane by 36&#176;. It was also found from cyclic voltammetry experiments in 0.5 M KOH, that the ionized monolayers of 4-dodecyloxymercaptophenol were 2.3 kJ/mol less stable than monolayers of 3-dodecyloxymercaptophenols. This finding suggests that hydrogen bonding and other intermolecular interactions in 4-dodecyloxymercaptophenol are greater than in 3-dodecyloxymercaptophenol. / Ph. D.

C-H bonds are easily the most common type of ordinary chemical bond and studying carbon acidity will help us understand and predict the reactivity of organic compounds. Carbon acidities are ranked using acidity scales. One of the most prominent is the Streitwieser Lithium Indicator (SLI) scale. The term "indicator scale" implies that acids have been measured against one another in sequential fashion. The SLI scale uses lithium ion as the conjugate-base counterion and THF as the solvent. Historically, the SLI scale has emphasized the characterization of weakly-acidic hydrocarbons. Prior to the work of our group, the strongest acid on the SLI scale has a pK value of about 10. Deck and Thornberry extended the scale to ca. pK = 0 by evaluating 23 perfluoroaryl-substituted cyclopentadiene and indene derivatives, using 19F NMR spectroscopy to determine the equilibrium constants of sequential acid-base reactions. This thesis describes the further extension of the SLI scale to ca. pK = −6. To achieve this result, a set of 11 tetrasubstituted cyclopentadienes were synthesized and their acidities evaluated sequentially with the goal of reaching a low pK value while minimizing the acidity ratio at each incremental step. The four ring substituents were combinations of pentafluorophenyl, perfluoro-4-tolyl, and perfluoro-4-pyridyl, electronegative groups listed in order of increasing electron-withdrawing power. The most acidic compound in the set was 1-pentafluorophenyl-2,3,4-tetrakis(tetrafluoro-4-pyridyl)cyclopentadiene, having pK = −5.99. Trends in the acidities of tetraarylcyclopentadienes are discussed including relative electron-withdrawing power of the three selected substituents, and conformational effects among pairs of regioisomeric cyclopentadiene derivatives. / Master of Science / Carbon acidity refers to the willingness of a carbon-hydrogen bond to release a hydrogen ion. C-H bonds are easily the most common type of ordinary chemical bond, so it makes sense that studying carbon acidity will help us understand and predict the reactivity of organic compounds. For the past several decades, emphasis in this area of research has focused on weak carbon acids, especially the simplest hydrocarbons like benzene and methane. This thesis aims in the opposite direction of synthesizing and measuring stronger and stronger carbon acids until we reach the theoretical limit for a given solvent. Because our research strategy is inherently incremental, compounds were synthesized and their acidities were measured, drawing close to the theoretical limit using tetrahydrofuran as the solvent.

Yes / Literature solubilities and NMR and IR studies have been used to obtain properties or descriptors of edaravone. These show that edaravone has a significant hydrogen bond acidity so that it must exist in solution partly as the OH and NH forms, as found by Freyer et al. Descriptors have been assigned to the keto form which has a low hydrogen bond acidity, and which is the dominant form in nonpolar solvents. Physicochemical properties of the keto form can be been calculated such as solubilities in nonpolar solvents, partition coefficients from water to nonpolar solvents, and partition coefficients from air to biological phases.

Thesis (MSc. Agriculture(Soil Science) -- University of Limpopo, 2018 / Soil acidity is one of the abiotic stress factors that greatly limit the productivity of crops on farmers’ fields. A greenhouse study was carried out over two summer growing seasons to evaluate the effect of lime and phosphorus (P) application rates on the growth, yield and root attributes of a determinate cowpea variety on acid soil. The experiment was laid out as a 4x5 factorial arrangement with 4 replications. Treatment factors comprised of variable rates of Vaalburg dolomitic lime (0, 2, 4 and 6 t ha-1) and P (0, 15, 30, 45 and 60 kg ha-1) using single super phosphate, 10.5% P. The two treatment factors were combined resulting in a total of 20 treatment combinations. Data collected included cowpea growth parameters, crop phenology, yield attributes and root characteristics. While cowpea plants with no P application consistently gave the least plant height, stem diameter, number and length of trifoliate leaves, the 6 t ha1 lime rate appears to be completely disadvantaged for all measured parameters with generally lower values than in soil filled pots without lime application. Results showed that soil pH was increased with 6 t ha-1 lime application while soil electrical conductivity (EC), percent of organic matter (OM) and total organic carbon (TOC) were all increased with increasing P and lime rates. All measured cowpea growth attributes such as plant height, stem diameter, number of trifoliate leaves, and leaf area were significantly increased (p≤0.05) with increasing P and lime rates. During the two planting seasons, P and lime application resulted in reduced (p≤0.05) duration to flowering, pod formation and physiological maturity. The 6 t ha-1 lime application produced higher number of pods (2.50) compared to the other rates. Application rates of 45 kg P ha-1 and 6 t ha-1 of lime produced superior number of seeds per pod with high values of (13.71) and (12.85), respectively. However, cowpea root attributes namely number of nodules per plant, the third branching root diameter, angle of adventitious root, tap root diameter at 5 and 10 cm, shallow and deep score were significantly increased at moderate P rate of 30 kg P ha-1. Overall, findings of this study revealed that application of both P fertiliser and lime were able to ameliorate the negative effect of P deficiency from soil acidity on the evaluated cowpea variety and promoted increased yield. Keywords: Acid soil, grain cowpea, P fertiliser, lime, growth, root characteristics, yield / National Research Foundation (NRF) and Department of Agriculture, Forestry and Fisheries (DAFF)