To see the other types of publications on this topic, follow the link: Aromatic system.
Dissertations / Theses on the topic 'Aromatic system'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Aromatic system.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Mancinelli, Michele <1981>. "Conformation and Stereodynamic of Hindered Aromatic System." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1344/2/michele_mancinelli_tesi.pdf.
Full textAbstract:
The preparation of conformationally hindered molecules and their study by DNMR and computational methods are my thesis’s core.
In the first chapter, the conformations and the stereodynamics of symmetrically ortho-disubstituted aryl carbinols and aryl ethers are described.
In the second chapter, the structures of axially chiral atropisomers of hindered biphenyl carbinols are studied.
In the third chapter, the steric barriers and the -barrier of 1,8-di-aylbiphenylenes are determined.
Interesting atropisomers are found in the cases of arylanthrones, arylanthraquinones and arylanthracenes and are reported in the fourth chapter.
By the combined use of dynamic NMR, ECD spectroscopy and DFT computations, the conformations and the absolute configurations of 2-Naphthylalkylsulfoxides are studied in the fifth chapter.
In the last chapter, a new synthetic route to ,’-arylated secondary or tertiary alcohols by lithiated O-benzyl-carbamates carrying an N-aryl substituent and DFT calculations to determinate the cyclic intermediate are reported. This work was done in the research group of Prof. Jonathan Clayden, at the University of Manchester.
2
Mancinelli, Michele <1981>. "Conformation and Stereodynamic of Hindered Aromatic System." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1344/.
Full textAbstract:
The preparation of conformationally hindered molecules and their study by DNMR and computational methods are my thesis’s core.
In the first chapter, the conformations and the stereodynamics of symmetrically ortho-disubstituted aryl carbinols and aryl ethers are described.
In the second chapter, the structures of axially chiral atropisomers of hindered biphenyl carbinols are studied.
In the third chapter, the steric barriers and the -barrier of 1,8-di-aylbiphenylenes are determined.
Interesting atropisomers are found in the cases of arylanthrones, arylanthraquinones and arylanthracenes and are reported in the fourth chapter.
By the combined use of dynamic NMR, ECD spectroscopy and DFT computations, the conformations and the absolute configurations of 2-Naphthylalkylsulfoxides are studied in the fifth chapter.
In the last chapter, a new synthetic route to ,’-arylated secondary or tertiary alcohols by lithiated O-benzyl-carbamates carrying an N-aryl substituent and DFT calculations to determinate the cyclic intermediate are reported. This work was done in the research group of Prof. Jonathan Clayden, at the University of Manchester.
3
Terraneo, G. "Simple model system to study sugar/aromatic interactions." Doctoral thesis, Università degli Studi di Milano, 2006. http://hdl.handle.net/2434/143397.
Full textAbstract:
A molecular scaffold was identified which enables the establishment of intramolecular interactions between a monosaccharide and a nearby phenyl ring. A group of molecules containing four different monosaccharides (glucose, galactose, N-acetyl-glucosamine and N-acetyl-galactosamine) was synthesized and used to investigate the extent and nature of this carbohydrate-arene interaction, as well as the effect on the overall 3D structure of the molecules involved. The sugar-aromatic distance was evaluated by rigorous NMR studies supported by molecular modeling, and found to be constant throughout the series, independent of the nature of the sugar, and of the conformational behaviour of the fragment connecting the two elements. Ab initio calculations at the B3LYP/DZV(2d,p) level of theory enable the analysis of the electronic nature of the interaction. The study shows that, given the opportunity, persistent intramolecular aromatic-sugar interactions can be established and can significantly influence overall molecular shape and energetics. These results have important implications in the design of structural mimics of oligosaccharides
4
Castelo, Alves Ferreira Frederico. "Membrane aromatic recovery system (MARS) : theoretical analysis and industrial applications." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409559.
Full text
5
Daisley, Gavin Rhys. "Membrane Aromatic Recovery System (MARS) : improved membranes and a further application." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508324.
Full text
6
Cameron, Grant William Wright. "A transport system for the uptake of aromatic carboxylates in Aspergillus." Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238930.
Full text
7
Dicken, Laura. "A Study of Polycyclic Aromatic Hydrocarbons During Combustion in an AFBC System." TopSCHOLAR®, 1997. http://digitalcommons.wku.edu/theses/302.
Full textAbstract:
The purpose of this study was to develop the on-line method of analysis which leads to the study of polycyclic aromatic hydrocarbons (PAHs) during combustion in an atmospheric fluidized bed combustor (AFBC) system. The study of PAHs is important because they may be produced upon the combustion of coal. The US EPA prioritizes PAHs as major pollutants due to their mutagenic and carcinogenic effects. Standards of PAHs were analyzed by injection into the gas chromatograph-mass spectrometer (GC-MS). These standards were then analyzed using the on-line method. Two coals were burned in the AFBC system and effluent samples were collected. These were analyzed with the GC-MS to see if there were any PAHs or chlorobenzenes present.
8
Addleton, Andrew Mark. "Microbial degradation of aromatic compounds in a Gravel Bed Hydroponic (GBH) system." Thesis, University of Portsmouth, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310474.
Full text
9
Chung, Ming Kei. "Assessment of phytotoxic effects of PAHs and DDTs in solid-phase system using microalgal bioassays." HKBU Institutional Repository, 2005. http://repository.hkbu.edu.hk/etd_ra/628.
Full text
10
Dastgir, Muhammad Ghulam. "The development of synthetic membranes and their performance in the Membrane Aromatic Recovery System (MARS)." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429374.
Full text
11
Li, Cheuk Fai. "Studies of flow injection system for micelle-assisted preconcentration of PAHs coupled with HPLC." HKBU Institutional Repository, 2009. http://repository.hkbu.edu.hk/etd_ra/1059.
Full text
12
Elie, Marc. "Use of an Activated Magnesium/cosolvent System for the Desorption and Degradation of Polycyclic Aromatic Hydrocarbons and Their Oxygenated Derivatives in Contaminated Soils." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5196.
Full textAbstract:
The contamination of soils, with polycyclic aromatic hydrocarbons (PAHs), remains a widespread environmental concern. In the past two decades, many physical, chemical and biological methods have been developed and evaluated for the degradation of PAHs. However, due to their low aqueous solubility, high sorption affinity, hydrophobicity and recalcitrance, the environmental remediation of PAHs in soil continues to be economically challenging. In addition to PAH contamination, the presence of oxygenated derivatives of PAHs (OPAHs), in soils, has increasingly become a concern due to their greater toxic properties compared to parent PAH compounds. To date, no investigations on OPAH-remediation methods have been presented in the literature. The use of zero-valent metals (ZVMs) has been reported for several halogenated contaminants in solution systems, but the effectiveness of ZVM to degrade sorbed PAHs and OPAHs has been rarely addressed. This present research focuses on the development of a combined technique for the feasible desorption and degradation of PAHs and OPAHs in soils. PAH and OPAH degradation efficiency, using activated magnesium (Mg) metal combined with an ethanol-ethyl lactate cosolvent (1:1 ratio), was initially examined in soil-free systems. This metal/cosolvent system demonstrated adequate degradation (above 80%) for high-molecular-weight (HMW) PAHs, which were subsequently converted into hydroaromatic compounds; while OPAHs were degraded and converted into hydroxylated or hydrogenated derivatives. Further soil-free studies revealed that the degradation rate was affected by the surface or reactive sites of the metal and that optimum degradation efficiency were obtained with Mg ball milled with graphite (Mg/C). In a bench-scale feasibility test, the efficacy of this system was assessed on a soil spiked with a mixture of three HMW PAHs compounds and three OPAHs compounds with amounts ranging from 0.033 mmol to 0.060 mmol. The experimental results show that 2 mL of an ethanol-ethyl lactate solvent mixture resulted in 58% to 85% extraction efficiency for the selected contaminants in 1 g of spiked soil, followed by 64 - 87% degradation efficiency of the extracted contaminants with 4.11 mmol of the activated metal. This activated-Mg/cosolvent system can be considered as a promising alternative method for ex situ remediation of PAH and OPAH-contaminated soils.Ph.D.
Doctorate
Chemistry
Sciences
Chemistry
13
Simpson, Christopher David. "Some aspects of the distribution and fate of polycyclic aromatic hydrocarbon contamination in the Kitimat fjord system." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25162.pdf.
Full text
14
Han, Wenjun. "An On-line Test for Polycyclic Aromatic Hydrocarbons in the Flue Gas from Coal Combustion in an FBC System." TopSCHOLAR®, 1999. http://digitalcommons.wku.edu/theses/781.
Full textAbstract:
Polycyclic Aromatic Hydrocarbons (PAHs) are environmental pollutants that have received considerable attention because of their carcinogenic and mutagenic effects. Due to the extensive amount of data suggesting the hazards of these compounds, 16 PAHs are on the Environmental Protection Agency (EPA) Priority Pollutant List. These compounds are often emitted into the atmosphere by way of combustion processes. Thus, analysis of these compounds during coal combustion is an important task. Three 1000-hour coal combustion burns were performed using the 0.1 MW (0.3 m) bench-scale Fluidized Bed Combustor (FBC) in the Combustion Laboratory at Western Kentucky University. The data for this thesis were collected from the second and third 1000-hour experiments. An in-situ sampling system was designed for 16 PAHs specified by EPA, which consisted of a glass wool filter, condenser, glass fiber filter, Teflon filter, and Tenax. The filters and Tenax were extracted by methylene chloride and hexane, respectively, followed by GC/MS analysis using the Selective Ion Monitoring (SIM) mode. The detection limits for each of the sixteen PAHs are as low as lppb. In this study, the effects of combustion temperature, combustion bed height, fluidizing velocity, excess air ratio, and the ratio of secondary air to primary air (air staging combustion) on the emissions of PAHs were studied. The results indicated that the emissions of PAHs in an FBC system were dependent on the combustion conditions. PAHs are mainly produced by incomplete combustion. Incomplete combustion results in larger PAHs with four or more benzene rings. High efficiency combustion results in smaller PAHs with two or three benzene rings.
15
Munir, Anjum [Verfasser]. "Design, development and modeling of a solar distillation system for the processing of medicinal and aromatic plants / Anjum Munir." Kassel : Universitätsbibliothek Kassel, 2010. http://d-nb.info/1007323116/34.
Full text
16
Young, Elizabeth A. "Second Messenger System Modulation of Aromatic L-Amino Acid Decarboxylase and Tyrosine Hydroxylase in Normal and MPTP Lesioned Mice /." The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487929230741091.
Full text
17
Karamat, Fazeelat. "Identification and functional characterization of the first two aromatic prenyltransferases implicated in the biosynthesis of furanocoumarins and prenylated coumarins in two plant families : Rutaceae and Apiaceae." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0029/document.
Full textAbstract:
Les furocoumarines constituent l'une des classes de métabolites secondaires dérivant de la voie de biosynthèse des phénylpropanoïdes. Elles ont été décrites comme étant des phytoaléxines mais sont également très largement utilisées par l'Homme pour leurs propriétés thérapeutiques. Un certain nombre d'études biochimiques ont été réalisées afin d'en comprendre la biosynthèse mais peu de choses sont connues concernant leur déterminisme moléculaire. Dans cette étude, nous nous sommes concentrés sur la caractérisation fonctionnelle de gènes appartenant aux prényltransférases aromatiques potentiellement impliquées dans cette voie de biosynthèse. Les prényltransférases catalysent la première étape de la voie de biosynthèse des furocoumarines linéaires ou angulaires. Elles permettent l'addition d'un groupement dimethylally pyrophosphate (DMAPP) sur l'umbelliférone. En utilisant SfN8DT-1, une prényltransférase aromatique récemment caractérisée, comme sonde, nous avons identifié 7 gènes candidats chez deux familles de plantes (Rutaceae et Apiaceae). Dans la mesure où il a été décrit que ces enzymes étaient des protéines membranaires, nous avons adapté un système d'expression hétérologue basé sur l'utilisation de N. benthamiana. Ce système a été validé par l'expression de deux protéines membranaires : un cytochrome P450 CYP98A22 et une prényltransférase déjà caractérisée SfN8DT-1. Nous avons ensuite utilisé ce système d'expression pour réaliser l'étude des 7 gènes nouvellement isolés. Ces travaux nous ont permis de caractériser la première umbelliferone prenyltransferase de Petroselinum crispum capable de catalyser in vitro et in vivo la prénylation du carbone 6 ou 8 de l'umbelliférone en présence de DMAPP permettant ainsi la synthèse respectivement de demethylsuberosin et d'osthenol. Par ailleurs, une étude réalisée in planta chez le persil a permis de mettre en évidence une relation positive entre le niveau d'expression du gène et la teneur en umbelliférone prénylée. L'étude de la surexpression du gène chez Ruta graveolens a permis de mettre en évidence un lien entre l'expression du gène et la disparition de l'umbelliférone. Enfin nous avons identifié la même activité pour une prényltransférase de Pastinaca sativa, ce qui nous amène à émettre l'hypothèse que l'étape de prénylation n'est pas une étape limitante dans la biosynthèse des furocoumarines angulaires, étant donné que le persil ne produit que des furocoumarines linéaires, tandis que le panais produit des furocoumarines linéaires et angulaires. L'utilisation de ces mêmes systèmes d'expression hétérologue de N. benthamiana et R. graveolens nous a également permis d'identifier une seconde prényltransférase aromatique capable de catalyser l'addition de géranylpyrophosphate (GPP) sur l'umbelliférone et sur l'esculétineFuranocoumarins constitute one of the classes of secondary metabolites deriving from the phenylpropanoid biosynthetic pathway. These molecules are described as phytoalexins in plants but are also used by humans for their pharmaceutical properties. A large number of biochemical studies were carried out to understand their biosynthetic pathway but little information was available concerning the genes involved in the pathway. In this study, we focused on the characterization of genes encoding for aromatic prenyltransferases which were described to be involved in this pathway. Prenlyltransferases catalyze the entry step to the linear or angular furanocoumarin pathway. Hence they catalyze the addition of a dimethylallyl pyrophosphate (DMAPP) prenyl moiety to umbelliferone. Using a recently characterized aromatic prenyltransferase (SfN8DT-1) as a probe, we isolated 7 different candidate genes from two plant families (Rutaceae and Apiaceae). As these enzymes were described as membrane bound proteins, we adapted a heterologous expression system made up of Nicotiana benthamian aand we validated its efficiency by using two membrane-associated enzymes: a cytochrome P450 (CYP98A22) and the already described prenyltransferase SfN8DT-1. Subsequently, this system was used to perform the functional characterization of the 7 newly identified proteins. This way we succeeded to characterize the first umbelliferone prenyltransferase of Petroselinum crispum that was able to catalyze both the 6-C and 8-C prenylation of umbelliferone with DMAPP producing demethylsuberosin and osthenol respectively. We made evidence that these reactions occurred both in vitro and in vivo. In addition, in planta studies performed in P.crispum showed a positive relationship between the gene expression level and the content of prenylated umbelliferone. The overexpression of this gene was investigated in Ruta graveolens and we could provide evidences of a link between the enzymatic activity and the disappearance of umbelliferone. We also reported a similar activity for a prenyltransferase isolated from Pastinaca sativa, which makes us assume that the prenylation step is not a rate limiting step in the biosynthetic pathway of angular furanocoumarins since parsley is producing only linear furanocoumarins whereas parsnip is producing both linear and angular furanocoumarins. In addition, using the same N. benthamiana and R. graveolens heterologous expression systems, we identified a second aromatic prenyltransferase able to catalyze the addition of geranyl pyrophosphate (GPP) both to umbelliferone and esculetin
18
Magron, Corinne. "Perfluoroalkylation of aromatic systems." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4634/.
Full textAbstract:
I. We have concentrated on the synthesis of aromatic systems containing CH(_2)R(_F) groups, where R(_F) is a bulky group derived from hexafluoropropene dimer, using fluoride ion induced methodology. A variety of procedures have been explored and methods of synthesis are described. We have made a major advance in this area by the simple expedient of extracting the polyfluoroalkylated products directly into commercially available perfluorinated fluids: FC-84 (bp 8O C), enabling simple purification. II. This new class of perfluoroalkylated derivatives has allowed us to explore some further chemistry. Synthesis and reactions are presented and the results are discussed in terms of electronic effects of the perfluoroalkyl group on the benzene ring. The unusual miscibility properties of fluorocarbon solvents have also prompted us to investigate the potential utility of these systems for dyes and catalysis. III. Synthetically useful perfluoroalkylated-s-triazines have been synthesised from 2,4,6-trifluoro-s-triazine, by fluoride ion induced reaction with hexafluoropropene. These systems so produced were extensively studied, and particular attention was paid to reactions with oxygen-centered nucleophiles. Model chemistry to demonstrate that attachment of perfluorocarbon groups to surfaces could be a useful form of treatment by using this methodology and was explored.
19
Romagnoli, Barbara. "Synthesis and characterisation of a novel class of chiral poly(aromatic aminde) dendrimers incorporating a C₃-symmetric core system derived from the α-amino acids L- and D-serine." Thesis, University of Reading, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250671.
Full text
20
Gordon, J. L. M. "Ipso attack of aromatic systems." Thesis, University of Canterbury. Chemistry, 1993. http://hdl.handle.net/10092/7859.
Full textAbstract:
This thesis concerns the chlorination reactions of a series of methyl and chloro substituted 4-chloro-6-methylphenols. The regioselectivity and mode of the chlorine addition reaction to the phenolic ring is examined with respect to the position of the substituents on the phenolic ring, and their properties of either donating or withdrawing electrons. It is shown that suppression of nucleophilic mechanisms of chlorine addition, which used to be achieved through the use of sodium acetate, can be accomplished more efficiently by the choice of acetic anhydride as a solvent.
Chlorine reacts with electron rich 2,6-dimethyl phenols by electrophilic mechanisms, with 2,3-addition appearing to be the favoured mode of reaction. This is illustrated by the reactions of two substituted phenols in Chapter Two.
Chapter Three describes the reactions of a dichloro methyl phenol which reacts with chlorine preferably by nucleophilic pathways. Electrophilic addition can be forced by the use of acetic anhydride, or by the addition of sodium acetate to the solvent, and the greater effectiveness of the former at suppressing nucleophilic addition is illustrated in this section. The stereochemistry of the chlorine addition is examined through the chlorination reactions of 2,4-dibromo-6-methyl phenol.
In Chapter Four, it is shown that nucleophilic attack of chloride ion is the preferred reaction mode of electron deficient trichloro methyl phenols. The two phenols discussed in this Chapter also illustrate the necessity of a vacant C3 ring position for nucleophilic addition to occur. Blocking this site with a chloro substituent slows the reaction drastically.
The behaviour of chlorine towards two dichloro dimethyl phenols is examined in Chapter Five. Again, the necessity of an unsubstituted C3 site for nucleophilic addition is demonstrated, with the switching of mechanism from nucleophilic with C3 vacant, to electrophilic with a methyl substituted C3 position.
Finally, use of Semi-Empirical calculations is made throughout this thesis, to estimate the relative stabilities of intermediate species and for a theoretical study of the interconversion of various cyclohexadienones by [1,5]-sigmatropic shifts of chlorine.
21
Müller, Britta Katrin [Verfasser]. "Systems biological investigation of aerobic and anaerobic aromatic catabolism in the bacterium Aromatoleum aromaticum EbN1 / Britta Katrin Müller." Braunschweig : Technische Universität Braunschweig, 2016. http://d-nb.info/1175818380/34.
Full text
22
Campbell, Smith Alison May. "Controlling directed metalation in aromatic systems." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610077.
Full text
23
Lewis, Zoe G. "Synthetic, spectroscopic and structural studies on carbametallaboranes containing aromatic and fused aromatic ring systems." Thesis, University of Edinburgh, 1991. http://hdl.handle.net/1842/15208.
Full textAbstract:
Chapter 1 gives an overview of carbaborane chemistry, including concepts of cluster bonding and slip distortions in carbametallaboranes derived from [7,8-nido-C2B9H11]2-. This is followed by an introduction to the transition metal chemistry of fused aromatic ligands, with specific reference to the similar bonding capabilities of these and carborane species. Finally, the structure of 3-(η5-C9H7)-3,1,2-closo-C2B9H11 (1) is discussed with rationalisation of the observed cisoid molecular conformation. Chapter 2 comprises two sections, A and B. Section A presents the syntheses and structures of three indenyl carbametallaboranes, 1-Ph-3-(η5-C9H7)-3,1,2-closoC2B9H10 (2), 1-(CH2OCH3)-3-(η5-C9H7)-3,1,2-closo-C2B9H10 (3) and 1,2-(CH2OCH3)2-3-(η5-C9H7)-3,1,2-closo-C2B9H9 (4). In 2 and 3 the indenyl ligand adopts a conformation analogous to that in 1, i.e. the indenyl ring junction carbon atoms are cisoid with respect to the cage carbon atoms. In 4 the presence of two ether substituents has resulted in the adoption of the 'next best' staggered conformation. A series of EHMO calculations performed on idealized models of 1-4 predict theoretical energy minimum conformations in broad agreement with those observed crystallographically. Section B describes the synthesis and structural determination of the first reported fluorenyl carbametallaborane complex, 3-(η5-C13H9)-3,1,2-closo-C2B9H11 (5). The molecular conformation has been rationalised in terms of the trans influence of the facial cage boron atoms, and is in full accord with that predicted by the results of EHMO calculations on an idealised model of 5.
24
Dickinson, John Andrew. "Electronic spectroscopy and conformations of aromatic systems." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363668.
Full text
25
Smith, Mathew D. "Reaction of hydroxyl radical with aromatic systems." Virtual Press, 2008. http://liblink.bsu.edu/uhtbin/catkey/1399191.
Full textAbstract:
The regioselectivity of the reaction of hydroxyl radical addition to toluene and naphthalene are examined in this study over the temperature range of 25°C-45°C. Also, the relative rates of reactivity as compared to benzene are determined for toluene, naphthalene, mesitylene, and p-xylene over the same temperature range. 2-(t-Butylazo)prop-2-yl hydroperoxide was used as the hydroxyl radical source and 1,1,3,3-tetramethylisoindolin-2-yloxyl was used as radical trap. For toluene the relative rates of addition were found to be 4 times greater for the ortho position versus the meta postion and 2 times greater for the para position versus the meta position, when the number of meta and para sites are taken into account.Department of Chemistry
26
Walker, Melinda. "Laser induced fluorescence spectroscopy of aromatic systems." Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282580.
Full text
27
Bruno, Carlo <1974>. "Electrochemistry of extended aromatic systems and nanostructures." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1036/1/Tesi_Bruno_Carlo.pdf.
Full text
28
Bruno, Carlo <1974>. "Electrochemistry of extended aromatic systems and nanostructures." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1036/.
Full text
29
Lodha, A. "Melt polyesterifications: kinetics in wholly aromatic systems." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 1996. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/3133.
Full text
30
Al-Bashir, Bilal. "Biodegradation of polycyclic aromatic hydrocarbons in soilwater systems." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59963.
Full textAbstract:
This study is concerned with the biodegradation of polycyclic aromatic hydrocarbons (PAHs), particularly the utilization of biological processes in the bioremediation of PAH-contaminated soils. In this regard, the effects of the contaminant bioavailability and the redox environment on the biodegradation process have been investigated.First, the mineralization of naphthalene in soil/water systems under denitrifying conditions has been studied. Results showed that naphthalene mineralization is influenced by its availability to the microbial population, which in turn is a function of the compound initial concentration, the sorption/desorption characteristics of the soil/contaminant complex and the organic content of the soil.
Second, the biodegradation of four PAH compounds, acenaphthene, acenaphthylene, fluorene and anthracene, in a soil/water system under four redox environments has been studied. Both aerobic and denitrifying environments supported appreciable PAH biodegradation rates. The denitrifying environment was chosen for a further experiment to investigate the performance of a bioreactor system in treating PAH-contaminated soils. Results showed that by enlarging the scale of the reactor by approximately eight times and simultaneously reducing the mixing intensity of the soil slurry, the biodegradation rates of the PAH compounds remained virtually unchanged.
31
Cargill, Matthew Robert. "Polyfluorinated aromatic systems for liquid crystal display applications." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/642/.
Full textAbstract:
This thesis is concerned with the syntheses of a range of polyfluorinated biphenyl ether derivatives for use as dopants in commercial LC materials, so that overall display performance may be improved. Reactions of hexa– and penta–fluorobenzene with sodium phenoxide in polar aprotic solvents (MeCN, THF) and under mild reaction conditions (45–50 °C, 4–65 h) afford moderate yields of pentafluorophenoxybenzene and 1,2,4,5–tetrafluoro–3–phenoxybenzene, respectively. SNAr reactions of sodium phenoxide with less electrophilic 1,2,3,4–tetra– and 1,2,3,5–tetra–fluorobenzene under microwave irradiation (150 °C, 30 mins) furnish good yields of 1,2,4–trifluoro–3–phenoxybenzene and 1,2,5–trifluoro–3–phenoxybenzene, respectively. Similar SNAr methodology is used to access a series of 1,2,4,5–tetra– and 1,2,4–tri–fluoro–3–(4–n–alkylphenoxy)benzene derivatives in good yield. A two–step SNAr–hydrodebromination procedure to access trifluorophenoxybenzene systems from highly electrophilic dibromotetrafluorobenzene derivatives is also developed, and provides a practical synthetic route to 1,2,4–trifluoro–5–phenoxybenzene. Finally, a three–step SNAr–diazotisation–reductive diazotisation pathway is developed for the syntheses of difluorophenoxybenzene derivatives, which are not accessible by direct SNAr reactions of sodium phenoxide with corresponding trifluorobenzene derivatives. The use of these polyfluorinated biphenyl ether systems as dopants for LC materials is assessed by a range of electro–optical measurements. Highly fluorinated nitrobenzene systems are compatible substrates for palladium–catalysed Suzuki–Miyaura and Heck–type cross–coupling reactions involving C–F bond activation. Cross–coupling reactions of pentafluoronitrobenzene with a range of boronic acids and protected ester equivalents bearing electron–withdrawing or electron–donating substituents in the meta– and para– positions, with respect to the C–B bond, are described. For example, Reaction of pentafluoronitrobenzene with 5,5–dimethyl–2–phenyl–1,3,2–dioxaborinane in the presence of catalytic quantities of Pd(PPh3)4 and using KF/alumina as the preferred base (DMF, 150 °C, 15 mins, μW) affords 2,3,4,5–tetrafluoro–6–nitrobiphenyl in good yield (80 %). The nitro group is crucial to the success of the cross–coupling processes and is believed to facilitate the oxidative addition step by directing the palladium catalyst into the adjacent C–F bond by a predominantly SNAr–type mechanism.
32
Wilkes, A. G. "Energy transfer studies on polyene and aromatic systems." Thesis, University of Nottingham, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376478.
Full text
33
Martin, Peter Arnold. "Nucleophilic substitution reactions of some polyhalogenated compounds." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6876/.
Full textAbstract:
Rate measurements for the reactions of a series of polyfluoro - and polychloro - pyridines with aniline and ammonia in 60/40 dioxan/water at 25ºC has shown that chlorine, when ortho and para to the position of attack, is activating with respect to fluorine, but at the position meta to the point of attack, chlorine and fluorine are virtually equivalent in their effect on reaction rate. The trifluoromethyl and nitrile groups were found to be activating relative to fluorine when ortho and para to the position of substitution and the nitrile group was thus found to be ortho/para directing. The ortho/para orienting effect of ring nitrogen was shown to be dominant in heterocyclic systems. It has been demonstrated for several different nucleophiles that nucleophilic attack in polyfluorinated heterocycles occurs so as to maximise the number of ortho and meta fluorines with fluorine being of little significance. Of the nucleophiles examined aniline and ammonia were found to be similar in their behaviour. Benzylamine however showed some propensity for substitution at positions ortho to ring nitrogen whilst N-methylaniline showed strong steric effects due to the N-methyl group, most notably when the heterocylic ring substituents were chlorine, trifluoromethyl and nitrile. Sodium was shown to have a 'salt effect' in the reactions of methoxide and phenoxide, and, a catalytic effect on the reactions of aniline affecting both the rate and position of substitution. The use of transition state, and molecular orbitals to explain the patterns of substitution is discussed. The trifluoromethylsilyl group was found to undergo nucleophilic attack at silicon and the series of mono, di and tri-fluoromethyl-pentafluorobenzenes were used to examine the concept of negative ion hyperconjugation.
34
Cornwall, Philip. "Heteroaromatic functionalization." Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252739.
Full text
35
CRAVEIRO, Nykon. "Hidrocarbonetos no sedimento superficial do sistema estuarino do Rio Formoso, nordeste do Brasil." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/18335.
Full textAbstract:
Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-02-16T14:23:09Z
No. of bitstreams: 2
license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)
DISSERTACAO-NYKON_CRAVEIRO_BIBLIOTECA-COMPLETA_SemAssinaturas.pdf: 2023918 bytes, checksum: ae7ded82175a687652e553dbed943897 (MD5)Made available in DSpace on 2017-02-16T14:23:09Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTACAO-NYKON_CRAVEIRO_BIBLIOTECA-COMPLETA_SemAssinaturas.pdf: 2023918 bytes, checksum: ae7ded82175a687652e553dbed943897 (MD5) Previous issue date: 2016-07-14
CNPq
A contaminação por hidrocarbonetos (HCs) do petróleo em regiões costeiras marinhas, como os estuários, é considerada uma das mais importantes e impactantes, devido aos danos que esses elementos podem ocasionar aos organismos e ao homem. O objetivo do presente estudo foi investigas, pela primeira vez, os hidrocarbonetos nos sedimentos superficiais do sistema estuarino do Rio Formoso (SERF), litoral Sul do estado de Pernambuco – Brasil. Os compostos de hidrocarbonetos alifáticos (HAs) foram determinados em cromatógrafo a gás (GC) Agilent Tecnologies 7820A, acoplado a um detector de ionização de chamas (DIC) e os compostos de hidrocarbonetos policíclicos aromáticos (HPAs) foram determinados no mesmo cromatógrafo, porém acoplado a um espectrômetro de massas 5975 (MS) em modo de monitoramento de íons selecionados (SIM). A concentração de alifáticos totais (∑Alif) nos sedimentos do SERF variou entre 1,37 e 126,64 μg g-1 peso seco (ps), com as concentrações de n-alcanos totais (Σn-Alc) entre 0,51 e 27,5 μg g-1 ps, oriundos principalmente de fontes biogênicas, como vegetais superiores. A concentração de HPAs (Σ16HPAs) variou entre 3,80 e 500,3 ng g-1 ps, provenientes de fontes petrogências e pirogênicas As concentrações de hidrocarbonetos alifáticos e aromáticos detectados nos sedimentos do sistema estuarino do Rio Formoso foram consideradas baixas, quando comparadas com outras áreas estudadas ao redor do mundo e aos índices propostos por estudos e agências reguladoras nacionais e internacionais, sugerindo um ambiente com pouco impacto sobre a biota. Contudo, a presença de compostos como HPAs é um indicativo de ação antrópica sobre o sistema, sendo importante a implantação e manutenção de um programa de monitoramento na área, quanto aos hidrocarbonetos, para avaliar os possíveis impactos que a presença desses compostos possam ocasionar sobre o SERF e garantir a conservação continuada de um estuário de tamanha importância ecológica, econômica e social.
The contamination by hydrocarbons (HCs) of oil in marine coastal regions, such as estuaries, is considered one of the most important and impactful due to the damage that these elements may cause to the bodies and man. The aim of this study was investigas for the first time, the hydrocarbons in the surface sediments of the estuarine system of the Formoso river (SERF), South coast of the state of Pernambuco - Brazil. Aliphatic hydrocarbon compounds (HAs) were determined on a gas chromatograph (GC) Agilent Technologies 7820A coupled to a flame ionization detector (FID) and polycyclic aromatic hydrocarbon compounds (PAH) were determined in the same chromatograph, however coupled a mass spectrometer 5975 (MS) in selected ion monitoring mode (SIM). The concentration of total aliphatic (ΣAlif) in SERF sediments ranged between 1.37 and 126.64 μg g-1 dry weight (dw), with total n-alkanes concentrations (Σn-Alc) between 0.51 and 27.5 μg g-1 dw, mainly from biogenic sources such as higher plants. The concentration of PAHs (Σ16HPAs) ranged from 3.80 to 500.3 ng g-1 dw, from petrogências sources and pyrogenic Hydrocarbon concentrations aliphatic and aromatic detected in the sediments of the estuarine system of the Formoso river were considered low compared with other areas studied around the world and the indices proposed by studies and national and international regulatory agencies, suggesting an environment with little impact on the biota. However, the presence of compounds such as PAHs is indicative of human action on the system, it is important to establishing and maintaining a monitoring program in the area, as hydrocarbons, to assess the possible impact that the presence of these compounds can cause on SERF and ensure the continued conservation of an estuary of such ecological, economic and social.
36
Jalali, Elnaz. "Regiospecific P-Bromination of Activated Aromatic Systems – Greener Approach." TopSCHOLAR®, 2017. http://digitalcommons.wku.edu/theses/1950.
Full textAbstract:
The halogenated derivatives of heterocyclic compounds (haloarenes) are highly utilized in many fields of chemistry, including drug discovery, medicinal, and material chemistry. There are a variety of ways to functionalize an aromatic system and introduce halogen substituent into the ring. However, electrophilic aromatic substitution (EAS) has been the focus of growing attention, particularly for electronrich substrates.
Electrophilic aromatic bromination protocols are one of the most important electrophilic aromatic substitution reactions. However, preparation of bromoarenes classically recommends the use of highly oxidative agents along with utilizing various metal catalysts in a halogenated solvent. The corrosive and toxic nature of these reagents and need of harsh conditions for these protocols make their utility less desirable in current practice. Furthermore, lack of regioselectivity for most substituted aromatics is the other distinguished drawback, since most products contain ortho/para directors which afford a mixture of isomers.
The innovation of our procedure for the bromination of various substituted aromatic compounds is twofold in that highly regiospecific para-bromination of activated aryls by treatment with NBS has been accomplished. Although various reaction mediums, such as cyclohexane, acetone, and acetonitrile has been used in this procedure, the significant high yields of the product formation along with the very short reaction times using acetonitrile make this approach more attractive. That this regiospecific p-substitution takes place under such mild conditions leads us to question whether it is EAS.
37
Stern, Jennifer E. Seinfeld John H. "Aerosol formation and growth in aromatic hydrocarbon/NOx systems /." Diss., Pasadena, Calif. : California Institute of Technology, 1988. http://resolver.caltech.edu/CaltechETD:etd-12282004-153051.
Full text
38
Mirajkar, S. P. "Mass spectrometry on some model aromatic and antiaromatic systems." Thesis(M.Sc.), CSIR-National Chemical Laboratory, Pune, 1986. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2217.
Full text
39
Kurata, Ryohei. "Studies on Electronic Properties of Nitrogen-and Boron-Containing π-Electron Systems." Doctoral thesis, 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225623.
Full textAbstract:
京都大学0048
新制・課程博士
博士(工学)
甲第20398号
工博第4335号
新制||工||1672(附属図書館)
京都大学大学院工学研究科分子工学専攻
(主査)教授 関 修平, 教授 今堀 博, 准教授 伊藤 彰浩, 教授 白川 昌宏
学位規則第4条第1項該当
Doctor of Philosophy (Engineering)
Kyoto University
DGAM
40
Giles, Robert G. "Some reactions of acyl cation equivalents with nucleophilic aromatic systems." Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/11087.
Full textAbstract:
Trimethyloxonium fluoroborate rapidly reacts with nitriles at elevated temperatures, to afford N-methylnitrilium salts. Subsequent reaction with π-excessive heterocyclic aromatic systems has been shown to give rise to iminium salts in moderate to excellent yields. The related imines may be obtained by deprotonation, and these compounds can be converted further by reduction or hydrolysis to secondary amines or ketones respectively. The reactions studied provide access to acylated indoles and pyrroles which are obtainable by other methods in inferior yields. The related reactions with carbocyclic aromatic systems were studied in an attempt to determine the range of heteroatom ring substituents which may be used.
41
Chen, Jing. "SOLUTION AND SOLID STATE INTERACTIONS BETWEEN IONIC π-SYSTEMS." UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_diss/289.
Full textAbstract:
Although attractive interactions between π systems (π-π interaction) have been known for many years, understanding of its origin is still incomplete. Quantitative measuring of π-stacking is challenging due to the weak nature of the π-π interaction. This dissertation aims at elucidating a quantitative conformational analysis by NMR ring current anisotropy of an organic compound capable of intramolecular π-stacking in solution and studying charge effects on the stacking of π-systems. This dissertation offers four contributions to the area. (1) A general approach to four-state, conformational analysis based on the magnetic anisotropy of molecules undergoing fast dynamic exchange is described. (2) Study unveiled the importance of charges in the conformation of a dication in the solution. (3) Novel aromatic salt pairs of triangulene derivatives with the delocalized cation-anion interaction were synthesized and studied. (4) Study unveiled ionic π-systems preferred face-to-face stacking due to strong cation-π and anion-cation attractions.
A general protocol for the application of magnetic anisotropy to quantitative multi-state conformational analysis of molecules undergoing fast conformational exchange was suggested in the current study. The reliability of this method of conformational analysis was checked by the mass balance. VT-NMR was also conducted to study the enthalpic parameters. This technique can be further used to study canonical interactions such as ion pairing, hydrogen boning, and molecular recognition.
In the current study, dependence of the probe conformations on the dispersive interactions at the aromatic edges between solvent and probes was tested by conformational distributions of the fluorinated derivatives (2b and 2c) of the probe molecule (1a). Solution and solid studies of these molecules put the previous conclusion drawn by the Cammers group in question. Current studies show that the dispersive interaction at the aromatic edge could not be the predominant force on the conformational changes in the probe molecule 1a during the fluoroalkanol perturbation. This study indicated that charges might be important in the formation of the folding conformations in the solution and solid state of 1a, 2b, and 2c. A contribution of this thesis was to prepare and study a conformational model that lacked charges. The previous molecules were charged.
The solid-state structures of pyridinium-derived aromatic rings from the CSD (Cambridge Structural Database) were studied to investigate the π-π interaction between cationic π-systems in solid state. Novel aromatic salt pairs of triangulene derivatives with the delocalized cation-anion interaction were synthesized to study the π-π interaction between two aromatic rings that carried opposite charges. This study showed that the interaction between ionic π-systems can be enhanced by cation-π and anion-cation attractions. The stackings of these π-systems introduce more overlap, closer packing and stronger atomic contact than that of the solid states of comparable neutral species. Cation-π and anion-cation attractions are synergistic in aromatic salts.
42
Dunn, Stephen Norman. "Free radical synthesis of new organofluorine systems." Thesis, Northumbria University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365437.
Full text
43
Rajuri, Venkataramana [Verfasser]. "Rational synthesis of tubular and belt-like aromatic systems / Venkataramana Rajuri." Kiel : Universitätsbibliothek Kiel, 2009. http://d-nb.info/1019867698/34.
Full text
44
Al-Bashir, Bilal. "Bioavailability of nitrogen-substituted polycyclic aromatic hydrocarbons in flooded soil systems." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28654.
Full textAbstract:
The sorption/desorption behavior in soil/water systems of $ sp{14}$C-radiolabeled naphthalene and nine of its nitrogen-substituted derivatives; quinoline, isoquinoline, quinoxaline, 1-aminonaphthalene, 2-aminonaphthalene, 1-amino-2-methylnaphthalene, 1-nitronaphthalene, 2-nitronaphthalene and 1-nitro-2-methylnaphthalene were investigated with respect to their physico-chemical properties and the type of interaction they form with soil organic and mineral matter. In turn, an investigation into the effect that sorption/desorption has on the bioavailability of these organic compounds and their mineralization kinetics was conducted.The non-polar naphthalene, the slightly polar quinoxaline and the three nitronaphthalene compounds sorbed through hydrophobic interaction giving rise to linear sorption isotherms that are typical of partitioning processes in which organic matter functions as a partition medium. Amino-naphthalenes, being polar and slightly basic, adsorbed through cation exchange, hydrogen bonding and formed coordination complexes at soil organic and mineral matter surfaces. Quinoline and isoquinoline, due to their relatively high dipole moment, intercalated the interlamellar space of layered-soil minerals. However, quinoline did not exhibit a specific type of interaction in the interlamellar region, while isoquinoline molecules adsorbed specifically, probably through surface protonation or coordinate covalent bonding with metal ions, and produced micelles upon sorption between the basal planes of clay particles. The discrepancy between the sorption behavior of quinoline and that of isoquinoline is attributed, in part, to the stronger hygroscopic nature of the former compound, its lower acidity constant and to the asymmetric shape of its molecules.
The desorption behaviors of naphthalene and 1-nitro-2-methylnaphthalene, both yielding concave up desorption isotherms, show a readily reversible component that gradually gives way to an irreversible one. The -CH$ sb3$ group, in the case of 1-nitro-2-methylnaphthalene, reduced hysteresis which is attributed to an increase in the hydrophobicity of the molecule and the steric effect that the methyl substitution has on hydrogen bonding. Desorption of quinoline and isoquinoline followed a hysteresis loop (concave down desorption isotherm) such that reversibility increased with decreasing soluble concentrations in the aqueous phase. Amino-naphthalenes adsorbed irreversibly at soil surfaces which is suggestive of strong interaction forces resembling those of a chemical reaction.
The mineralization of all studied compounds gave rise to hyperbolic mineralization curves comprising two phases; an initial fast one followed by a second slow phase with gradually declining rates.
Quinoline maximum mineralization rates were first order with respect to soluble concentrations and the amounts of quinoline mineralized initially coincided with the soluble fraction. In contrast, the amounts of isoqoinoline mineralized during the fast phase exceeded its corresponding fractions in solution. Mineralization exhibited saturation-type kinetics (Michaelis-Menten type) which probably indicates that the biodegradation of isoquinoline was mediated by its sorption in the micellar form.
Finally, naphthalene maximum mineralization rates correlated linearly with total concentrations (soluble and sorbed) and the total amounts mineralized during the fast phase exceeded substantially the soluble fraction. (Abstract shortened by UMI.)
45
Okere, Uchechukwu Victor. "Biodegradation of polycyclic aromatic hydrocarbons in "pristine " soils from different environmental systems." Thesis, Lancaster University, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.656326.
Full textAbstract:
Global soils have the capacity to act as a sink for polycyclic aromatic hydrocarbons (PAHs) and subsequently as a secondary source making soil/PAH interactions important to environmental PAH levels. A number of physical, chemical and biological processes determine P AH fate in soil but microbial degradation is the most important. Biodegradation depends on bioavailability, soil organic matter, water and nutrient content, temperature and previous exposure to PAHs. Globally, environments differ and soils from different geographic regions differ in their properties and PAH concentrations. While the importance of diffuse P AH contamination of soils is widely acknowledged in literature, most studies on P AH biodegradation in soils have been conducted on soils contaminated from a P AH point source. The aims of this project were to investigate the indigenous biodegradation of PAHs in pristine soils from different geographic locations as well as what environmental factors are most significant in the development of PAH biodegradation potential in pristine soils. Pristine soils used include soils from Antarctica, Norway, UK and Tibet. Levels of PAHs in all the soils were low and properties like soil organic matter, nutrients and water content were different. P AH degrading bacteria were present in all the soils studied irrespective of low PAH concentrations. Temperature was found to affect both the rates and extents of P AH degradation in the Antarctic soils. Results also suggest that the effect of temperature on adaptation of indigenous microbes to PAH degradation might be more important than that of lack of exposure. Further works suggested include the identification of individual P AH -degrading bacteria in these background soils and investigating the effect of increasing soil P AH-contact time in low organic matter background Antarctic soils.
46
Fort, Eric Henry. "Developing Methods for Growing Single-Chirality Carbon Nanotubes and Other Aromatic Systems." Thesis, Boston College, 2010. http://hdl.handle.net/2345/1531.
Full textAbstract:
Thesis advisor: Lawrence T. ScottThe work described herein stems from an effort to develop a method for growing single-chirality carbon nanotubes from small hydrocarbon templates using a Diels-Alder cycloaddition/rearomatization strategy. Current technologies are incapable of producing significant amounts of homogeneous carbon nanotubes; therefore, much research has been put into the development of aromatic templates (belts and bowls), from which one type of nanotube might be grown (Chapter 1). Since no such functional template had yet been synthesized, the work in this dissertation developed reagents and methods for forming new benzene rings on aromatic test systems that would be analogous to the rim of a growing nanotube (Chapters 2 and 4). Theoretical investigations relating to nanotube dimensions (Chapter 3) were undertaken and paired with experimental work that would take into consideration the changing properties of growing tubes (Chapter 5). The test systems used for discovering new reagents for growth also became functional platforms for studies of new reactivity of polycyclic aromatic hydrocarbons (PAHs), such as bay-region oxidation (Chapter 6) and progress toward the synthesis of soluble graphene ribbons (Chapter 7). This PAH work also resulted in the observation of unique solid state properties in the crystal form (Chapter 8) and novel reactivity, generating five-membered rings by Scholl reactions of tethered PAHs (Chapter 9). Additional considerations for future nanotube templates and fullerene precursors also bore scrutiny (Chapter 10)
Thesis (PhD) — Boston College, 2010
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
47
Gumus, Selahaddin. "Secondary Electronic and Solvent Effects on Regiospecific P-Bromination of Aromatic Systems." TopSCHOLAR®, 2018. https://digitalcommons.wku.edu/theses/3031.
Full textAbstract:
Bromoarenes are important aromatic building blocks that are commonly used to synthesize various functional compounds in pharmaceutical, agrochemical and related industries.1,2 This great demand for bromoarenes makes their preparation a widely studied area of synthetic organic chemistry. However, further understanding of the reactivity and regiochemistry of aromatic functionalization reactions is still necessary, as much about the secondary substitution and solvent effects remain unknown.
Resonance Theory is a widely used theoretical model to predict the regiospecifity and reactivity of the bromination of various aromatic compounds.3 The reactivity and regiospecificity of many substituted aromatic compounds is well explained using resonance theory.4 However, kinetic understanding of the p-bromination of halosubstituted aromatic compounds has not been investigated to the best of our knowledge.5,6In this thesis, the reactivity and regiospecifity of the p-bromination of activated secondary substituted aromatic compounds as well as media effects on the process will be discussed.
Synthesizing bromoarenes has been accomplished using many different experimental setups.7-11 N-bromosuccinimide is the most highly utilized electrophilic aromatic brominating agent. Many of the NBS- based aromatic bromination reactions have been reported using strong acids, strong bases, halogenated solvents, nonpolar solvents and polar solvents alike.12 The bromination reactions reported herein were performed using two different solvents, acetonitrile and acetone, to investigate the effects of solvent polarity on p-bromination. Although acetonitrile is one of the most commonly used solvents in the p-bromination of aromatic compounds, acetone has not been investigated.
48
BRUNO, GIOVANNA. "QUANTUM OBSERVABLES OF OPEN-SHELL SYSTEMS. A THEORETICAL STUDY." Doctoral thesis, Università degli Studi di Milano, 2022. http://hdl.handle.net/2434/936434.
Full textAbstract:
This PhD thesis reports original research results concerning the development of theoretical models and computational protocols for the quantification and analysis of two of the most important quantum observables of open-shell systems: the electron spin density and the phosphorescence energy gap. In the first part, a comprehensive theory of the electron spin density topology
is proposed for the first time [1]. Several new notions (spin density critical points, molecular spin graphs, spin density basins, spin maxima and spin minima joining paths etc.) and descriptors (local and integral spin polarization indeces, basin average spin density etc.) are introduced. This analysis reveals that the spin density topology, based on precise mathematical notions, can unveil precious information on the physical structure of spin-polarized systems. In particular, it enables to describe and quantify spin polarization and delocalization mechanisms and, at the same time, to evaluate the dependence of spin density distributions on the adopted level of theory. In the second part instead, the performance of the domain-based local pair natural orbital (DLPNO) variant of the “gold standard” CCSD(T) method for the prediction of phosphorescence energies of aromatic chromophores is investigated for the first time [2]. An extensive analysis of both accuracy and computational cost of the main parameters of the method (basis set, triples correction approximation, dimension of PNOs space) is conducted. Two procedures, the Gold DLPNO-CCSD(T) aimed at maximizing the accuracy and the Silver DLPNO-CCSD(T) aimed at minimizing the computational cost, which result in an excellent agreement with experimental data, are proposed.
1. G. Bruno, G. Macetti, L. Lo Presti and C. Gatti, “Spin Density Topology,” Molecules, 25, 3537, 2020.
2. G. Bruno, B. de Souza, F. Neese, and G. Bistoni, “Can domain-based local pair natural orbitals approaches accurately predict phosphorescence energies?,” Phys. Chem. Chem. Phys., 24, 14228–14241, 2022.
49
Azman, Nurul Aini Binti Mohd. "Investigation of the antioxidant properties of five aromatic plants in model food systems." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/335274.
Full textAbstract:
In this PhD it has been analyzed the antioxidant activity of five plants: Camelia sinensis, Gentian lutea, Betula pendula, Convolvulus arvensis and Arctostaphylos uva-ursi.
An Electronic Paramagnetic Resonance has been tuned up to determine the antiradical activity of white tea against the methoxy radical using ferulic acid as a standard. It has been proven that the components with more antiradical activity, against the methoxy radical, are the ones with the gallate group, EGCG and ECG.
Active ingredients of the Gentian root have been obtained with hydroalcoholic extraction and their antioxidant activity has been demonstrated in both in vitro methods and food models. The antiradical activity of such extracts was determined by FRAP, DPPH, TEAC and ORAC assays. The lyophilized extract, added to the ecological beef meat in a proportion of 2% (by mass), inhibited the meat oxidation (measured by TBARS assay) in high oxygen content atmospheres (80% in volume) as well as in low oxygen content ones (20% in volume). The simultaneous addition of ascorbic acid (0.5% by mass) resulted in significant improvements in color and stability. The lyophilized extract (0.5% by mass) also inhibited oxidation in model systems, oil-in-water emulsions, stored in forced oxidation conditions and constant agitation. The protein BSA addition (0.1% by mass) showed synergic effect and increased the emulsion stability against oxidation. HPLC quantitative analysis found that gentian contained secoiridoid-glycosides (gentiopiocroside and sweroside) and the post-column addition of ABTS cationic radical demonstrated the scavenging activity of each of its compounds.
For Convolvulus and Betula, the effect of the solvent polarity in the total polyphenol extraction (by the Folin Ciocalteau assay) was determined. The 50% ethanol extract was the best performer.
The scavenging activity of the Convolvulus extract was analyzed by TEAC, FRAP and ORAC assays and against methoxy radical (by EPR). Furthermore, lyophilized extract was added to minced meat hamburgers in different proportions (0.1 and 0.3% by mass). They were stored in a modified atmosphere (80% of O2 and 20% of CO2). Lastly, an edible gelatin film, with Convolvulus extract, was designed. All the assays showed capacity to protect the hamburgers against oxidation.
The antiradical activity of the Betula extract was also determined by TEAC, ORAC and FRAP assays and against methoxy radical (by EPR). Some of its phenolic acids were identified by HPLC. Hamburgers, with a proportion of 0.1% and 0.3% by mass of the lyophilized extract, were made and stored under refrigeration (4ºC) and in a modified atmosphere (80% of O2 and 20% of CO2). Colour and percentage of metmyoglobin changes were analyzed as well as the oxidation degree (by TBARS assay). Both percentages provided significant improvements in all the studied parameters.
The last part of this thesis was focused in the study of Arctostaphylos uva-ursi. The scavenging activity against ABTS+ and methoxy radical was determined (by EPR). A percentage of 0.1% by mass of the lyophilized extract was added to oil-in-water emulsions. Oxidation was measured by VP and TBARS. There was a significant delay in oxidation. Extract was incorporated to edible gelatin films with 0.1% by mass. If such a film protects the hamburger, its life is increased.
In conclusion, all five plants presented in this study have antioxidant activity (in the used proportions) that made them suitable to formulate new foods, more stable over time against oxidation without using the controversial synthetic antioxidants. Moreover, they will be able to provide additional advantages (incorporating natural antioxidants), which would provide functional foods.Se ha analizado la actividad antioxidante de cinco plantas: Camelia sinensis, Gentian lutea, Betula pendula, Convolvulus arvensis y Arctostaphylos uva-ursi. Se ha puesto a punto, con el té blanco, la Resonancia Paramagnética Electrónica (EPR) para determinar la actividad antiradicalaria frente al radical metoxi, usando como patrón el ácido ferúlico. Se ha demostrado que los componentes del té con más actividad antiradicalaria, frente a los radicales metoxi, son los que tienen el grupo galato, EGCG y ECG. Se han obtenido, por extracción hidroalcohólica, los principios activos de la raíz de genciana y se ha demostrado su actividad antioxidante tanto en métodos in vitro como en modelos de alimentos. La actividad antiradicalaria de dichos extractos se determinó por FRAP, DPPH, TEAC y ORAC. El liofilizado del extracto, añadido a la carne de ternera ecológica en proporción 0,2 % (en masa), inhibió la oxidación de la carne (medida por TBARs), tanto en atmósferas de alto contenido en oxígeno (80% en volumen) como de bajo contenido (20% en volumen). La adición simultánea de ácido ascórbico (0,5% en masa) produjo mejoras significativas en el color y en la estabilidad. El extracto liofilizado (0,5 % en masa) también inhibió la oxidación en sistemas modelo, emulsiones de aceite en agua, almacenadas en condiciones de oxidación forzada y con agitación constante. La adición de la proteína BSA (0,1 % en masa) mostró efecto sinérgico y aumento la estabilidad de la emulsión frente a la oxidación. El análisis cuantitativo mediante HPLC mostró que la genciana contenía glucósidos secoiridoides (gentiopiocrosido y swerosido) y la adición post-columna del radical catiónico ABTS, demostró la actividad antiradicalaria de cada uno de sus compuestos. Para Convulvuvus y Betula se determinó el efecto de la polaridad del disolvente en la extracción de los polifenoles totales (por el método de Folin Ciocalteau). El extracto de etanol al 50% fue el que obtuvo mejores resultados. Se analizó la actividad antiradicalaria del extracto de Convulvuvus mediante el TEAC, el FRAP, el ORAC y frente al radical metoxi (por EPR). Además se añadió el extracto liofilizado a hamburguesas de carne picada en diferentes proporciones (0,1 y 0,3 % en masa). Se almacenó en atmósfera modificada (80% de O2 y 20% de CO2). Finalmente se diseñó un film comestible de gelatina con el extracto de Convulvuvus. Todos los ensayos mostraron capacidad de proteger las hamburguesas frente a la oxidación. Se determinó la actividad antiradicalaria del extracto de Betula por TEAC, ORAC, FRAP y frente al radical metoxi (por EPR). Se identificaron por HPLC algunos de sus ácidos fenólicos. Se hicieron hamburguesas con una proporción de 0,1% y 0,3%, en masa, del extracto liofilizado y se almacenaron en refrigeración (4ºC) y en atmósfera modificada (80% O2 y 20% CO2). Se analizó el cambio de color y el cambio en el porcentaje de metamioglobina, así como el grado de oxidación (a través del TBARs). Los dos porcentajes proporcionaron mejoras significativas en todos los parámetros estudiados. La última parte de esta tesis se centró en el estudio de la Arctostaphylos uva-ursi. Se determinó la actividad antiradicalaria frente al ABTS·+ y frente al radical metoxi (por EPR). Se añadió a emulsiones de aceite en agua un porcentaje de 0,1 % en masa del extracto liofilizado. Se midió la oxidación por VP y TBARs. Se produjo un retraso significativo en la oxidación. Se incorporó extracto a films comestibles de gelatina con 0,1 % en masa. Si dicho film protege la hamburguesa, aumenta su vida útil. En conclusión, las 5 plantas presentadas en este estudio tienen una actividad antioxidante (en las proporciones utilizadas) que las hace aptas para formular nuevos alimentos, más estables en el tiempo frente a la oxidación sin el uso de los controvertidos antioxidantes sintéticos. Además podrán proporcionar ventajas adicionales (incorporación de antioxidantes naturales), lo que permitiría obtener alimentos funcionales.
50
Roth, Friedrich. "Electronic structure of selected aromatic hydrocarbon systems investigated with electron energy-loss spectroscopy." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-106800.
Full textAbstract:
Organic materials with fascinating/intriguing electronic properties have been the driving force for many research activities in the past, and in particular for important progress in materials science covering both new functional materials as well as theoretical developments. In addition, charge transfer, i. e., the addition or removal of charges to or from molecules in organic solids is one route to modify and control their electronic properties. Recently, the discovery of superconductivity in several alkali metal intercalated hydrocarbon systems (picene, phenanthrene, coronene and 1,2;8,9-dibenzopentacene) with rather high transition temperatures has opened a new chapter in organic material science as well as solid-state physics.
The search for a microscopic understanding of the mechanism that drives materials superconducting always has initiated a large number of scientific activities, and there are numerous examples where these activities have provided major advancement. A basic foundation of this understanding is the knowledge of the electronic properties of the material under investigation.
In this context, this thesis reports first, very detailed insight into the electronic structure of both undoped as well as potassium doped picene, coronene and 1,2;8,9-dibenzopentacene using electron energy-loss spectroscopy (EELS) as main experimental method. Additionally, also photoemission spectroscopy experiments have been performed to investigate the occupied electronic density of states close to the chemical potential. In order to learn more about the electronic structure we have compared the results we obtained from EELS and photoemission spectroscopy with theoretical calculations based on Density functional theory (DFT) using the local-density approximation (LDA).
We identify the peculiar case of very close lying conduction bands that upon doping harbour the electrons that form the Cooper-pairs in the superconducting state. Moreover, the presented data display substantial changes in the electronic excitation spectrum upon doping, whereas in the doped case the appearance of one new peak (for picene) and several new peaks (for coronene and 1,2;8,9-dibenzopentacene) in the former optical gap is reported. By using a Kramers–Kronig analysis (KKA) it is possible to gain information about the nature of this doping introduced excitations. In particular, in case of picene, the new low energy feature can be assigned to a charge carrier plasmon. Interestingly, this plasmon disperses negatively upon increasing momentum transfer, which deviates significantly from the traditional picture of metals based on the homogeneous electron gas. The comparison with calculations of the loss function of potassium intercalated picene shows how this finding is the result of the competition between metallicity and electronic localization on the molecular units.
Furthermore, core level excitation measurements show the reduction of the lowest lying C 1s excitation feature, which clearly demonstrates that potassium intercalation leads to a filling of the conduction bands with electrons. Additionally, the measurements of potassium intercalated 1,2;8,9-dibenzopentacene clearly indicate the formation of particular doped phases with compositions K_xdibenzopentacene (x = 1, 2, 3), whereas the data suggest that K_1dibenzopentacene has an insulating ground state with an energy gap of about 0.9 eV, while K_2dibenzopentacene and K_3dibenzopentacene might well be metallic, because of the absent of an energy gap in the electronic excitation spectra.
Interestingly, a comparison of the photoemission as well as EELS spectra of undoped 1,2;8,9-dibenzopentacene and pentacene reveal that the electronic states close to the Fermi level and the electronic excitation spectra of the two materials are extremely similar, which is due to the fact, that the additional two benzene rings in 1,2;8,9-dibenzopentacene virtually do not contribute to the delocalized pi molecular orbitals close to the Fermi level. This close electronic similarity is in contrast to the behavior upon potassium doping, where evidence for a Mott state has been reported in the case of pentacene.
A comparison of the low energy excitation spectra of chrysene with picene (phenacenes) as well as tetracene with pentacene (acenes) crystals reveal a significant difference between the former and the latter two materials. While for the phenacenes (zigzag arrangement) the excitation onset is characterized by up to five weak excitation features with only small anisotropy and without visible Davydov splitting within the a*, b*-planes, the acene (linear arrangement) spectra are dominated by a large excitation close to the onset and a sizable Davydov splitting. The presented data show further that the spectral shape of the pentacene excitation spectrum provides clear evidence for a large admixture of molecular Frenkel-type excitons with charge-transfer excitations resulting in excited states with a significantly mixed character. This conclusion is in good agreement with recent advanced calculations which predicted a charge-transfer admixture to the lowest singlet excitation which is significantly dependent upon the length of the acene molecules. Moreover, also for picene and chrysene we observe differences which point towards an increased charge-transfer contribution to the singlet excitation spectrum in the former.
Finally, investigations of the electronic properties of undoped and potassium doped chrysene, a close relative of picene, show that the doping introduced changes are in a similar range such as observed in case of picene. Interestingly, due to the analogy between the observed changes in the electronic structure upon potassium doping between chrysene and picene and further similarity in the crystal structure we speculate that chrysene is a promising candidate for another aromatic hydrocabon superconductor.