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1
Zeng, Xiaofeng. "Mechanisms for Solvolytic Elimination and Substitution Reactions Involving Short-lived Carbocation Intermediates." Doctoral thesis, Uppsala University, Organic Chemistry, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2565.
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Solvolysis reactions of a range of tertiary substrates in largely aqueous solvents were studied in such respects as β-deuterium kinetic isotope effects, linear free energy relationships and stereochemistry.
Solvolysis of the fluorene derivatives 9-methyl–9-(2´-X-2´-propyl)fluorene (1-X, X = Cl, Br, OOCCF3) involves a very short-lived carbocation intermediate. The fraction of alkene is increased by addition of general bases, which can be expressed by a Brφnsted parameter β = 0.07. The kinetic deuterium isotope effects vary with solvent composition in a way which is not consistent with a common carbocation intermediate which has time to choose between dehydronation and addition of a solvent water molecule.
In the absence of bases, the reaction of 4-chloro-4-(4´-nitrophenyl)pentan-2-one (2-Cl) proceeds through a short-lived carbocation intermediate yielding 4-(4´-nitrophenyl)-2-oxopent-4-ene (2-t-ne)as the main elimination product. Addition of acetate ion and other weak bases results in the base-promoted E2 (or E1cb) reaction to give (E)-4-(4´-nitrophenyl)-2-oxopent-3-ene (2-E-ne) and (Z)-4-(4´-nitrophenyl)-2-oxopent-3-ene(2-Z-ne). There is no evidence for a water-promoted E2 (or E1cb) reaction.
The stereochemistry studies of elimination from (R,S and S,R)-[1-(3´-fluoro)phenyl-2-methyl]cyclopentyl-p-nitrobenzoate (3-PNB) and its (R,R and S,S)isomer 3´-PNB and (R,S and S,R)-[1´-(3´´-fluoro)phenyl-2´-methylcyclopentyl]-2,2,2-trifluoroacetate(3-OOCCF3) exclude the concerted pericyclic elimination mechanism for formation of the alkene 1-(3´-fluoro)phenyl-2-methylcyclopentene(3-m-ne). The effects of added thiocyanate ion and halide ions on the solvolysis reaction are discussed.
Mass spectrometry analysis showed complete incorporation of the labeled oxygen from solvent water into the product 2-hydroxy-2-phenyl-3-butene (4-OH), confirming that it is the tertiary carbon-oxygen bond that is broken in the acid-catalyzed solvolysis of 2-methoxy-2-phenyl-3-butene (4-OMe). The mechanism for the dominant formation of the less stable 4-OH is discussed.
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Chung, Lung Wa. "Computational studies of the reaction mechanisms and stereochemistry of metal-mediated organic reactions /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202006%20CHUNG.
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Hayden, Amy Elizabeth. "Computational studies of mechanisms and reactivities of organic reactions." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1905657311&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Ji, Pengju. "Kinetics and mechanisms of organic reactions in liquid ammonia." Thesis, University of Huddersfield, 2011. http://eprints.hud.ac.uk/id/eprint/10033/.
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The rate constants for the reactions of a variety of nucleophiles reacting with substituted benzyl chlorides in liquid ammonia (LNH3) have been determined. To fully interpret the associated linear free-energy relationships, the ionisation constants of phenols ions in liquid ammonia were obtained using UV spectra. These equilibrium constants are the product of those for ion-pair formation and dissociation to the free ions, which can be separated by evaluating the effect of added ammonium ions. There is a linear relationship between the pKa of phenols in liquid ammonia and those in water of slope 1.68. Aminium ions exist in their unprotonated free base form in liquid ammonia and their ionisation constants could not be determined by NMR. The rates of solvolysis of substituted benzyl chlorides in liquid ammonia at 25 oC show a Hammett ρ of zero, having little or no dependence upon ring substituents, which is in stark contrast with the hydrolysis rates of substituted benzyl halides in water, which vary 107 fold. The rate of substitution of benzyl chloride by substituted phenoxide ions is first order in the concentration of the nucleophile indicative of a SN2 process, and the dependence of the rate constants on the pKa of the phenol in liquid ammonia generates a Brønsted βnuc = 0.40. Contrary to the solvolysis reaction, the reaction of phenoxide ion with 4-substituted benzyl chlorides gives a Hammett ρ = 1.1, excluding the 4-methoxy derivative, which shows the normal positive deviation. The second order rate constants for the substitution of benzyl chlorides by neutral and anionic amines show a single Brønsted βnuc = 0.21 (based on the aqueous pKa of amine), but their dependence on the substituent in substituted benzyl chlorides varies with a Hammett ρ of 0 for neutral amines, similar to that seen for solvolysis, whereas that for amine anions is 0.93, similar to that seen for phenoxide ion. The rates of aromatic nucleophilic substitution reactions in liquid ammonia are much faster than those in protic solvents indicating that liquid ammonia behaves like a typical dipolar aprotic solvent in its solvent effects on organic reactions. Nitrofluorobenzenes (NFBs) readily undergo solvolysis in liquid ammonia and 2-NFB is about 30 times more reactive than the 4-substituted isomer. Oxygen nucleophiles, such as alkoxide and phenoxide ions, readily displace fluorine of 4-NFB in liquid ammonia to give the corresponding substitution product with little or no competing solvolysis product. Using the pKa of the substituted phenols in liquid ammonia, the Brønsted βnuc for the reaction of 4-NFB with para-substituted phenoxides is 0.91, indicative of the removal of most of the negative charge on the oxygen anion and complete bond formation in the transition state and therefore suggests that the decomposition of the Meisenheimer σ-intermediate is rate limiting. The aminolysis of 4-NFB occurs without general base catalysis by the amine and the second order rate constants generate a Brønsted βnuc of 0.36 using either the pKa of aminium ion in acetonitrile or in water, which is also interpreted in terms of rate limiting breakdown of Meisenheimer σ-intermediate. Nitrobenzene and diazene are formed as unusual products from the reaction between sodium azide and 4-NFB which may be due to the initially formed 4-nitroazidobenzene decomposing to give a nitrene intermediate, which may dimerise and be trapped by ammonia to give the unstable hydrazine which then yields nitrobenzene. We have developed a method for the amination of aryl halides in liquid ammonia using copper (I) catalysis which enables direct synthesis of a number of primary amines with excellent yields. This method does not require strong base and ligands as additives and the amination in liquid ammonia has exclusive selectivity for the formation of primary amines, even under relative higher temperature. The amount of catalyst required for the reaction is relatively lower than that generally used, and the convenience of products separation with liquid ammonia as reaction medium indicate its potential industrial application. The preliminary mechanistic investigation indicates that the rate of the amination is first order dependence on the concentration of copper (I) catalyst, and the formation of triamminecopper (I)-aryl ring intermediate is probably the rate limiting step in liquid ammonia. Due to strong coordination of solvent molecules to the copper (I) ion, the kinetics of the reaction are generally insensitive to the addition of other conventional ligands in liquid ammonia. The copper (I) catalysed 1,3-Huisgen cycloaddition reaction of azide and alkynes (CuIAAC) in liquid ammonia requires less catalyst than those in conventionally used solvents. The excellent yield, exclusive selectivity, and most importantly, the ease of separation of the product indicate the potential advantages of using liquid ammonia as the solvent for this reaction. The preliminary mechanistic investigation suggests that CuIAAC reaction in liquid ammonia is a stepwise process with the initial formation of copper (I)-acetylide ion complex, followed by its combination with copper (I) coordinated azide.
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Hammar, Peter. "Quantum Chemical Studies of Mechanisms and Stereoselectivities of Organocatalytic Reactions." Doctoral thesis, KTH, Teoretisk kemi (stängd 20110512), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11616.
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As the field of organocatalysis is growing, it is becoming more important to understand the specific modes of action of these new organic catalysts. Quantum chemistry, in particular density functional theory, has proven very powerful in exploring reaction mechanisms as well as selectivities in organocatalytic reactions, and is the tool used in this thesis. Different reaction mechanisms of several organocatalytic reactions have been examined, and we have been able to exclude various reaction pathways based on the calculated reaction barriers. The origins of stereoselection in a number of reactions have been rationalized. The computational method has generally reproduced the experimental stereoselectivities satisfactorily. The amino acid-catalyzed aldol reaction has previously been established to go through an enamine intermediate. In the first study of this thesis the understanding of this kind of reactions has been expanded to the dipeptide-catalyzed aldol reaction. The factors governing the enantioselection have been studied, showing how the chirality of the amino acids controls the conformation of the transition state, thereby determining the configuration of the product. In the cinchona thiourea-catalyzed Henry reaction two reaction modes regarding substrate binding to the two sites of the catalyst have been investigated, showing the optimal arrangement for this reaction. This enabled the rationalization of the observed stereoselectivity. The hydrophosphination of α,β-unsaturated aldehydes was studied. The bulky substituent of the chiral prolinol-derived catalyst was shown to effectively shield one face of the reactive iminium intermediate, thereby inducing the stereoselectivity. The transfer hydrogenation of imines using Hantzsch esters as hydride source and axially chiral phosphoric acid catalyst has also been explored. A reaction mode where both the Hantzsch ester and the protonated imine are hydrogen bonded to the phosphoric acid is demonstrated to be the preferred mode of action. The different arrangements leading to the two enantiomers of the product are evaluated for several cases, including the hydride transfer step in the reductive amination of α-branched aldehydes via dynamic kinetic resolution. Finally, the intramolecular aldol reaction of ketoaldehydes catalyzed by guanidinebased triazabicyclodecene (TBD) has been studied. Different mechanistic proposals have been assessed computationally, showing that the favoured reaction pathway is catalyzed by proton shuttling. The ability of a range of guanidines to catalyze this reaction has been investigated. The calculated reaction barriers reproduced the experimental reactivities quite well.QC 20100719
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Hao, Weifang. "The Mechanisms of Hydride Exchange, Organic Combination and Displacement Reactions." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1226.
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The primary aim of this dissertation was to seek the answer to the question: “Is the single transition-state model appropriate for the fundamental reactions in organic chemistry?” The goal was accomplished by performing enormous kinetic data collection and detailed mechanistic analysis on several typical fundamental organic chemical reactions. Three new methodologies for differentiating between a simple one-step and complex multi-step mechanism were developed and extensively confirmed during the application in the kinetic studies of all of the reaction discussed in this dissertation. The three methods consist of (1) half-life dependence of kapp, (2) sequential linear pseudo-first-order correlation, and (3) revised instantaneous rate constant analysis. A detailed kinetic investigation of the formal hydride transfer reaction of NADH models [N-benzyl-1,4-dihydronicotinamide (BNAH) with Nmethylacridinium (MA+) and N-methyl-9,10-dihydroacridine (MAH) with tropylium ion (Tr+)] confirmed that both these reactions take place in more than one step and involve kinetically significant reactant complex intermediates, which are noncovalentlly bound intermediates. Computations at the M06-2x/6-311++G(d,p) level provided the structure of the reactant complex intermediate. A reinvestigation of the formal hydride transfer reaction of 1-benzyl-3- cyanoquinolinium ion (BQCN+) with N-methyl-9,10-dihydroacridine (MAH) in acetonitrile (AN) confirmed that the reaction takes place in more than one step and revealed a new mechanism that had not previously been considered. It was observed that even residual oxygen under glove box conditions initiates a chain process leading to the same products. The combination reactions studied include the reaction between a carbocation and an anion as well as the reaction of trans-β-nitrostyrene with nitroethide ion. Conventional pseudo-first-order analysis as well as instantaneous rate constant analysis confirmed that the combination reactions do not follow the simple one-step mechanism. The SN2 displacement of halide ions by the 4- nitrophenoxide ion was also investigated and the kinetic data are inconsistent with the concerted single transition-state model.
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Power, Nicholas Patrick. "Kinetics and mechanisms of reactions of N-arylsulfonyl derivatives of imines." Thesis, University of Ulster, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267781.
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Tan, Kristine Joy Wei Mei. "Thiyl radical reactions with alkynes in the absence and presence of oxygen." Connect to thesis, 2009. http://repository.unimelb.edu.au/10187/7036.
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This thesis is concerned with the reactions of sulfur-centred radicals and alkynes. The first objective of this work was to extend the scope of “self-terminating radical cyclisations” to sulfur-centred radicals, such as thiyl radicals. Preliminary experiments revealed that the reaction of thiyl radicals with alkynes was sensitive to residual oxygen. In the absence of oxygen, the reactions of photochemically generated phenylthiyl radicals with cyclodecyne (1) resulted in three isomeric sulfides, which were identified through a combination of techniques. (1S,6S)-2-phenylthiobicyclo[4.4.0]decane (trans-49a, unknown stereochemistry at C2) was identified by synthesis of an authentic sample, while the structure of (1S,2R,6S)-2-phenylthiobicyclo[4.4.0]decane (cis-49a1) was determined by X-ray analysis of the corresponding crystalline sulfone, cis-69. The third sulfide, (1S,2S,6S)-2-phenylthio-bicyclo[4.4.0]decane (cis-49a2), was assigned based on computational studies.In addition, the reactions of benzylthiyl, tert-butylthiyl and allylthiyl radicals with cyclodecyne (1) were investigated. Various sources of thiyl radical generation were utilized, such as the photolysis of disulfides and thiols, hydrogen atom abstraction of thiols using radical initiators, as well as thiol autoxidation in the presence of oxygen. The radical cascade initiated by the addition of thiyl radicals to alkyne 1 was typically terminated by either reduction or disproportionation, whereas “self-termination” was only observed in one particular instance where the tert-butylthiyl radical was generated by autoxidation. However, this was only a minor pathway.
The second objective of this work was to investigate the reactions of thiyl radicals with alkynes in the presence of oxygen. For this purpose, phenylthiyl radicals were generated in the presence of diphenylacetylene (89) and molecular oxygen. Benzil (91), an α-diketone, and 1,2-diphenyl-2-(phenylthio)ethanone (93), an α-ketosulfide, were formed. The novel thiyl radical-mediated oxidation of diphenylacetylene to benzil mediated proceeds under mild and metal-free conditions, using various methods of thiyl radical generation. The product ratio of diketone to ketosulfide varied with the reaction conditions. Under photochemical conditions, benzil was formed but its photodegradation was also observed. Using autoxidation, moderate to good yields of both diketone 91 and ketosulfide 93 were obtained, although the product ratios varied with solvent and reaction conditions. Diketone 91 was the major product when the thiyl radical was generated electrochemically. Following investigation of the reaction mechanism using experimental and computational studies, the phenylthiyl peroxyl radical was identified as the key reactive intermediate. This represents the first synthetic application of thiyl peroxyl radicals.
Using autoxidation conditions, the oxidation was explored using substituted aromatic thiyl radicals, e.g. 2,6-dimethylbenzene, 2,4,6-tri-tert-butylbenzene, 4-methoxybenzene and 4-nitrobenzene thiyl radicals. Except for the case of 4-methoxybenzene thiyl radicals, where generation of the thiyl radicals was inefficient, diketone 91 was formed as the dominant product. This oxidation of alkynes to ketones, via thiyl radical-mediated activation of oxygen, was then applied to cyclodecyne (1). Bicyclic ketones 7/8 were found as the major products under photochemical conditions, while sulfides 152/trans-49a were the dominant products under autoxidation conditions. Bicyclic ketones 7/8 were formed due to the intramolecular radical processes directed by the transannular strain of the ten-membered carbon framework. Only trace amounts of the cyclic α-diketone 151 were detected under autoxidation conditions.
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Demirtas, Ibrahim. "Synthesis and mechanisms of reactions of substituted N-tritylamines and related compounds." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389591.
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El-Kaddar, Yousef Younis. "Organosilicon reaction mechanisms." Thesis, University of Sussex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375169.
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This thesis is concerned with the preparation and reactions of some highly sterically hindered organosilicon compounds, mainly of the type TeiSiMe2X where Tsi denotes the (Me3Si)3C group. The first detailed study of the reactions of TsiS1Me20CN has shown that reactions with NaN3 in MeOH or KSCN or KOCN in MeCN give exclusively the corresponding TsiSiMe2X compounds (X = N3, NCS, or NCO), whereas those with other salts, viz. LiCl, CsF, KSCN, and KOCN, give the TsiSiMe2X species along· with other products, including in many cases TsiSiMe2NCO and TsiSiMe20H (from traces of water), and (in MeOH) TsiSiMe20Me. The reaction with MeOH alone was never found to give less than 10% ot TslSiMe20H, along with the expected TsiSiMe20Me, however carefully the MeOH was dried. The extreme sensitivity of the cyanate towards water was illustrated by the fact that the rate ot solvolysis in 'dry' MeOH was increased by~. 90% by addition of 0.05 vol-% of H2o, and the hydroxide was the sole product, whereas the rate for the triflate TsiSiMe2- OS02CF3 was increased by only 13% and the product was a 60:40 mixture of TsiSiMe20Me and TsiSiMe20H. The rate constant for the triflate increased linearly with the water concentration but that of the cyanate did not. The presence of NaOMe in MeOH led to rapid isomerization of the cyanate to the isocyanate, TsiSiMe2NCO, with the rate of isomerization being proportional to the base concentration: a possible explanation of this effect of base is suggested. Isomerization catalysed by ICI in CC14 was found to be of ca. second order with respect to both the cyanate and the IcI: A detailed kinetic study has been carried out of the the reactions of TsiSiMe2X compounds, with X c I, Br, Cl, or ON02' with various alkali metal salts, MY, viz. NaN3' CsF, KSCN, and KOCN in MeOH and with KSCN in MeCN. For X • I, Br, or Cl, the reactions have been shown to be much more complex than was previously thought, the compounds TsiSiMe20Me, TsiSiMe20H, and (Me3Si}2CHSiMe2oMe commonly being formed along with TsiSiMe2Y. The order of effectiveness of the salts in the formation of TsiSiMe2Y is CsF > NaN3 > KSCN > KOCN, except that for X - I the order for CsF and NaN3 is reversed. Approximate values of the activation parameters have been obtained: the activation entropies have very high negative values, consistent with formation of a very crowded transition state. The nitrate is markedly more reactive even than the iodide, and gives cleaner conversions into TsSiMe2Y compounds: the activation energies are much lower and the activation entropies much more negative than those tor the halides. Reactions of the compounds (Me3Si)2C(SiMe2H)(SiMe2Cl) with alkali metal salts have been shown to be much faster than those of TsiSiMe2Cl, casting doubt on an earlier suggestion that the ease of solvolysis of the former chloride might be due to anchimeric assistance by y-H.
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Li, Zhao. "The Kinetics and Mechanisms of Some Fundamental Organic Reactions of Nitro Compounds." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1407.
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The central topic of this dissertation is to seek the answer to the question: Is the single transition state model appropriate for (1) the proton transfer reactions of nitroalkanes and (2) the aromatic nucleophilic reactions of trinitroarenes? If not, what are the real mechanisms? This objective has been accomplished by careful kinetic and mechanistic studies which take advantage of modern digital acquisition of absorbance - time data, combined with extensive new data analysis of results from pseudo-first-order kinetic measurements.
Several new analysis procedures for pseudo-first-order kinetics that are capable of distinguishing between single-step and multi-step mechanisms have been introduced and intensively confirmed during the application in the kinetic study of the target reactions. The procedures include (1) half-life dependence of apparent rate constant, (2) sequential linear pseudo-first-order correlation, (3) approximate instantaneous rate constant analysis, and (4) time-dependent apparent kinetic isotope effects.
Various conventional and nonconventional pseudo-first-order kinetic analyses of the reactions of nitroalkanes in aqueous solutions revealed that the reactions are complex and involve kinetically significant intermediates. The spectral evidence for the formation of reactive intermediates was obtained by carrying out the kinetic experiments at the isosbestic points where changes in reactant and product absorbance cancel. The apparent deuterium kinetic isotope effects studies indicated that the deuterium kinetic isotope effects are not associated with the formation of the intermediates. The observations of anomalous Brønsted exponents previously found for this reaction series could be rationalized well with the complex mechanisms proposed in this work, which indicate that the nitroalkane anomaly does not exist, but arises from an interpretation based upon the incorrect assumption that the reactions follow a simple one-step mechanism.
Simulations revealed that the generally accepted competitive mechanism was not appropriate to describe the Meisenheimer complex formation during the reaction of 2,4,6-trinitroanisole with methoxide ion in methanol. This conclusion is supported by the conventional pseudo-first-order kinetic analysis. A reversible consecutive mechanism that accounts for the kinetic behavior has been proposed, which involves an intermediate dianion complex that is formed reversibly from the initial 1,3-σ-complex, and then eliminates methoxide ion to form the 1,1-σ-complex product.
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Matsunaga, Aiko. "Secondary organic aerosol formation from radical-initiated reactions of alkenes development of mechanisms /." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://proquest.umi.com/pqdweb?index=0&did=1899476651&SrchMode=2&sid=2&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1269361334&clientId=48051.
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Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 10, 2010). Includes bibliographical references. Also issued in print.
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Conner, Keyanna M. "Gas Phase Studies of Organic Reaction Mechanisms." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/4032.
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The competition between substitution (SN2) and elimination (E2) in nucleophilic reactions of alkyl halides has had a profound influence on the development of physical organic chemistry and remains an important testing ground for identifying reactivity patterns in gas-phase organic chemistry. Here, the competition between substitution and elimination, as well as the regioselectivity of E2 reactions have been examined in the gas phase. By doing so, the intrinsic reactivity patterns can be probed in the absence of solvation effects.
The SN2 and E2 reactions of a large set of alkyl bromides with varying substitution patterns at the α- and β-carbons were studied in the gas phase using naphthoate and phenoxide-based dianion nucleophiles. The experiments were performed in a quadrupole ion trap mass spectrometer equipped with electrospray ionization. The experimental work was supported by calculations at the MP2/6-31+G(d,p)//MP2/6-31+G(d) level. The naphthoate is a weaker base and leads to more products from the SN2 pathway. In accord with generalizations from condensed-phase results, primary bromides generally prefer substitution pathways and secondary bromides prefer eliminations. In the gas phase, polarizability is more important, and the highest SN2 reactivity is observed when the β-carbon is 2° - steric crowding from β-substituents is not as significant for un-solvated nucleophiles. In addition, the data confirms that alkyl substituents at the β-carbon have a greater accelerating effect on E2 reactions than those at the α-carbon. Finally, computed data based on lowest enthalpy pathways provide poor descriptions of the reactions of the larger alkyl bromides and are skewed toward crowded systems that offer stabilizing, nonbonded interactions at the expense of conformational freedom.
An investigation of regiochemical preferences of E2 reactions was also explored by synthesizing and analyzing the product distributions of a set of deuterium-labeled compounds capable of Saytzeff and Hofmann elimination. Gas-phase reactions of these substrates with dianion nucleophiles indicate that as expected, there is a preference for the Saytzeff product, which is also preferred in solution. This is the first study of E2 regioselectivity in the gas phase for a simple alkyl system.
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Brown, J. W. "Studies of heterocyclic reaction mechanisms." Thesis, Bucks New University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356206.
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Ruggiero, Guiseppe D. "Theoretical modelling of organic reaction mechanisms in solution." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301536.
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Last, Deborah J. "Laboratory studies of the products, mechanisms and kinetics of heterogeneous reactions on organic aerosol proxies." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491664.
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Aerosol particles have a significant impact on atmospheric processes through interacting directly with solar radiation, influencing cloud cover by acting as cloud condensation nuclei and by providing a surface on which heterogeneous reactions can take place. This thesis describes the development of an Aerosol Flow Tube (AFT) system with FT-IR detection for the study of heterogeneous processes occurring on aerosols. The major structural components, gas handling, particle generation, size distribution characterisation, and collection systems, and infrared optics are detailed, and high quality spectra of a range of inorganic, organic, and mixed inorganic-organic aerosols presented. Concurrent to the development ofthe AFT-FTIR system, a variety of analytical techniques were employed to investigate the ozonolysis of solution phase and thin film proxies. Infrared spectroscopy and mass spectrometry identified acids, aldehydes, esters, and ketones as products of the reaction, some of these being high molecular weight (HMW) compounds. These were concluded to be formed by combinations of Criegee intermediates (CI) with acid and aldehyde functionalities, leading to HMW products through a variety of linear and branching polymerisation pathways. Evidence was found of additional reaction pathways for CIs in the presence of aromatic rings, the nature of which bears further investigation. The distribution ofHMW products was observed to change with increased ozone exposure, leading to an increased concentration ofcyclic peroxides, suggesting some oxidation or decomposition of the initially formed aacyloxyalkyl hydroperoxides (AAHP) and peroxyhemiacetallinkages. The kinetics ofthe heterogeneous reaction of ozone with unsaturated organics was investigated in thin films in an ATR-IR cell and aerosols in the AFT. In the thin film studies a reactive uptake coefficient of (6.8±OA) xl 0-5 was obtained for oleic acid, an order of magnitude or so lower than that observed by most other researchers, whilst maleic acid and anthracene oxidation was found to be too slow to reliably study under the same conditions, but in the presence of oleic acid reactive uptake coefficients were found to be enhanced by factors of 6 and 10 respectively. In the AFT the decay of oleic acid aerosol was found to be well modelled by assuming a diffusion limited reaction, with reactive uptake coefficient (y) of 8.3xlO-4, in excellent agreement with other studies. The ozonolysis of anthracene coated on ammonium sulphate particles and as an internally mixed aerosol with oleic acid was investigated, and despite the considerable experimental challenges in studying such systems, the increased reactivity ofanthracene in the presence of oleic acid was again observed.
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Yu, Wenyuan. "Reaction Mechanisms and Synthesis of Oxidized Lipids." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1377387469.
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Ladhams, Zieba Meagan. "Teaching and learning about reaction mechanisms in organic chemistry." University of Western Australia. School of Biomedical and Chemical Sciences, 2004. http://theses.library.uwa.edu.au/adt-WU2005.0035.
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[Truncated abstract] This study was carried out to investigate the teaching and learning processes occurring in the topic of reaction mechanisms in three tertiary level organic chemistry courses and focussed on investigating perceptions about the importance of teaching and learning about reaction mechanisms and about the difficult aspects of the topic .... In the organic chemistry courses under investigation, students achieved many of the explicitly stated aims that their lecturers identified. The students rarely achieved implicit outcomes anticipated by the lecturer. Lecturers demonstrate a tendency to use particular structural representations when discussing certain types of reaction process. The study identified that students commonly use these same types when working through particular reaction processes. In addition, it was found that the use of a particular structure could cue students into thinking about only one type of reaction process taking place in a given reaction. The use of language that is consistent with a consideration of only single reaction particles was also commonly observed in lectures. While this can be adequate in some circumstances, other aspects of reaction processes are better considered in terms of multiple reaction particles ... The project proposes an integrated model, which takes into account the many levels (macroscopic, single particle molecular, multiple particle molecular and intramolecular) involved when describing reaction processes. It is felt that a consideration of the levels discussed in this model is useful when teaching and learning about reaction mechanisms.
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Davies, R. P. "The elucidation of organic reaction mechanisms involving lithium reagents." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598341.
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Lithium reagents are used to effect key deprotonation steps in numerous organic syntheses. In doing so they are often highly specific. However, little is known about how they function, the reasons for their high selectivity, and the natures of the lithiated organics present prior to work-up. This thesis seeks to redress this lack of structural knowledge of lithiated intermediates. It has been by isolating the intermediates in a variety of reactions involving lithiated organic reagents, establishing their precise identities, and studying their structures both in the solid and in solution that the author has been able to present this insight into the true reaction mechanisms involved and the source of any observed specificities. The reaction intermediates, whose syntheses and characterisation are described within this text, are all lithium complexes of the form [(R-)Li+.yL]n or [(R2-)2Li+]n where the lithium cation is bound to an organic anion (R- or R2) through one or more carbon centres and/or through electronegative heteroatoms (typically N, O or S). The lithium cation is often also bound to a Lewis base donor (L) which is a neutral but polar complexant. Chapter 1 gives a general introduction into the structural chemistry of organolithium and lithiated organic compounds and complexes, as well as a synopsis of their use in organic synthesis. General experimental methods are described in Chapter 2, and the synthesis and characterisations of all the complexes and compounds discussed (within Chapters 4 and 5) are presented in Chapter 3. Chapter 4 contains a detailed discussion on the origin of the regioselectivity exhibited in the -NC(OLi)R directed electrophilic substitution reactions of lithium amides (Section 4.1) and the -CO2Li directed electrophilic substitution reactions of lithium carbamates (Section 4.2). Finally, Chapter 5 looks into how deprotonation reactions using lithium reagents could actually proceed. This has been accomplished by studying the deprotonation of model phosphine oxide systems by lithium reagents both experimentally and theoretically using ab initio M.O. calculational results (Section 5.1), and also by studying the effects of reacting a simple organic molecule (Ph2NH) with an excess of lithiating reagent (t-BuLi and nBuLi)(Section 5.2).
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Lu, Mei. "Mass Spectrometric Study of Electrochemical and Organic Reaction Mechanisms." Ohio University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1437474195.
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Rastogi, A. K. "The study of Friedel-Crafts type reaction mechanisms." Thesis, Open University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377344.
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Revell, John Bernard. "Reactions of Some Cyclomanganated Compounds with C-Nitroso Compounds, Allenes, and Ketenimines." The University of Waikato, 2008. http://hdl.handle.net/10289/2275.
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eta2-(5-Methoxy-2-acetylphenyl)tetracarbonylmanganese (30) was reacted with 2-methyl-2-nitrosopropane (31) to form 2-acetyl-5-methoxy-N-(tert-butyl)aniline(43) in low yield. Attempts to improve the yield by varying the solvent were unsuccessful. Substrate 30 was reacted with nitrosodurene and orthomanganated triphenylphosphine sulfide was reacted with 2-methyl-2-nitrosopropane (31), however no new compounds were characterised in either case. Acetylallene (55) was reacted with 30. Electrospray ionisation-mass spectrometry(ESI-MS) provided evidence for the insertion of one and two molecules of 55 into the Mn-C bond of 30 to form the products tentatively identified as 56 and 57. The reaction of orthomanganated triphenylphosphine sulfide with acetylallene was attempted but no new compounds were characterised. In order to extend the study to ketenimines, the synthesis of the diphenylketene N-(p-tolyl)imine was attempted by the dehydration of N-(p-tolyl)diphenylacetamide under a variety of conditions, but it was not isolated in useful quantities. A single preliminary study of the reaction of diphenylketene N-(p-tolyl)imine with 30 gave an intense green solution, but no products were isolated.
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Cheong, Paul Ha-Yeon. "Quantum mechanical investigations of the mechanisms and selectivities of synthetic organic reactions from organocatalysis to transition metal catalysis to substrate controlled asymmetric reactions /." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1481668381&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Teuten, Emma L. "Radical mechanisms in the nitrosation of N, N-dialkylanilines." free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3074447.
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McKenna, Eugene Gerard. "The stereochemistry and mechanism of Wittig reactions of phosphonium and arsonium ylide anions." Thesis, Queen's University Belfast, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335560.
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Jonsson, Stefan. "The mechanism of Formyl-Coenzyme A transferase, a Family III CoA transferase, from Oxalobacter formigenes." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0007068.
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Manta, Bianca. "Quantum Chemical Studies of Enzymatic Reaction Mechanisms." Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-141321.
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Computer modeling of enzymes is a valuable complement to experiments. Quantum chemical studies of enzymatic reactions can provide a detailed description of the reaction mechanism and elucidate the roles of various residues in the active site. Different reaction pathways can be analyzed, and their feasibility be established based on calculated energy barriers. In the present thesis, density functional theory has been used to study the active sites and reaction mechanisms of three different enzymes, cytosine deaminase (CDA) from Escherichia coli, ω-transaminase from Chromobacterium violaceum (Cv-ωTA) and dinitrogenase reductase-activating glycohydrolase (DraG) from Rhodospirillum rubrum. The cluster approach has been employed to design models of the active sites based on available crystal structures. The geometries and energies of transition states and intermediates along various reaction pathways have been calculated, and used to construct the energy graphs of the reactions. In the study of CDA (Paper I), two different tautomers of a histidine residue were considered. The obtained reaction mechanism was found to support the main features of the previously proposed mechanism. The sequence of the events was established, and the residues needed for the proton transfer steps were elucidated. In the study of Cv-ωTA (Paper II and Paper III), two active site models were employed to study the conversion of two different substrates, a hydrophobic amine and an amino acid. Differences and similarities in the reaction mechanisms of the two substrates were established, and the role of an arginine residue in the dual substrate recognition was confirmed. In the study of DraG (Paper IV), two different substrate-binding modes and two different protonation states of an aspartate residue were considered. The coordination of the first-shell ligands and the substrate to the two manganese ions in the active site was characterized, and a possible proton donor in the first step of the proposed reaction mechanism was identified.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.
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Assabumrungrat, Suttichai. "Mechanisms and modelling of gas separations through ceramic membranes in chemical reaction processes." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/8151.
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Zhang, Hongkui. "1,3-dipolar cycloadditions of α, β-unsaturated sultone and sultams." HKBU Institutional Repository, 2004. https://repository.hkbu.edu.hk/etd_ra/532.
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Zhang, Yafen. "Ultrahigh Vacuum Studies of the Reaction Kinetics and Mechanisms of Nitrate Radical with Model Organic Surfaces." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/78003.
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Detailed understanding of the kinetics and mechanisms of heterogeneous reactions between gas-phase nitrate radicals, a key nighttime atmospheric oxidant, and organic particles will enable scientists to predict the fate and lifetime of the particles in the atmosphere. In an effort to acquire knowledge of interfacial reactions of nitrate radical with organics, model surfaces are created by the spontaneous adsorption of methyl-/vinyl-/hydroxyl-terminated alkanethiols on to a polycrystalline gold substrate. The self-assembled monolayers provide a well-defined surface with the desired functional group (-CH3, H2C=CH-, or HO-) positioned precisely at the gas-surface interface. The experimental approach employs in situ reflection-absorption infrared spectroscopy (RAIRS) to monitor bond rupture and formation while a well-characterized flux of NO3 impinges on the organic surface. Overall, the reaction kinetics and mechanisms were found to depend on the terminal functional group of the SAM and incident energy of the nitrate radical (NO3). For reactions of the H2C=CH-SAM with NO3, the surface reaction kinetics obtained from RAIRS reveals that the consumption rate of the terminal vinyl groups is nearly identical to the formation rate of a surface-bound nitrate species and implies that the mechanism is one of direct addition to the vinyl group rather than hydrogen abstraction. Upon nitrate radical collisions with the surface, the initial reaction probability for consumption of carbon-carbon double bonds was determined to be (2.3 ± 0.5) -- 10-3. Studies of reactions of HO-SAM with the effusive source of NO3 suggest that the reaction between NO3 and the HO-SAM is initiated by hydrogen abstraction at the terminal - 'CH2OH groups with the initial reaction probability of (6 ± 1)-- 10-3. An Arrhenius plot was obtained to measure the activation energy of the H abstraction from the HO-SAM. Further, for reactions of the HO-SAM with the high incident energy of NO3 molecules created by molecular beam, the reaction probability for H abstraction at the hydroxyl terminus was determined to be ~0.4. The significant increase in the reaction probability was attributed to the promotion in the ability of NO3 abstracting hydrogen atom at the methylene groups along hydrocarbon chains. The reaction rates of NO3 with the model organic surfaces that have been investigated are orders of magnitude greater than the rate of ozone reactions on the same surfaces which suggests that oxidation of surface-bound organics by nighttime nitrate radicals may play an important role in atmospheric chemistry despite their relative low concentration. X-ray photoelectron spectroscopy (XPS) data suggests that oxidation of the model organic surfaces by NO3 leads to the production of organic nitrates, which are stable for a period time. In addition, the effect of background gases on reactions of NO3 with model organic surfaces needs further investigations at atmospheric pressures. The results presented in this thesis should help researchers to predict the fate and environmental impacts of organic particulates with which nitrate radicals interact.Ph. D.
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Tchernook, Ivan. "Strategies for Computational Investigation of Reaction Mechanisms in Organic and Polymer Chemistry Using Static Quantum Mechanics." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-198756.
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This thesis presents computational studies of problems in the organic and polymer chemistry. The state-of-the art quantum chemical methods are used to gain further insight into the origin and the nature of the reactions in three different organic and polymer systems. The research questions are conceptually approached by identifying the key aspects. Then an appropriate strategy for the quantum chemical modeling is developed.
In the scope of the polymer chemistry, the novel synthesis technique of nanostructured materials, the so-called twin polymerization, is investigated. Using three model systems of increasing complexity the influence of the anion (trifluoroacetate) in the reaction system is investigated. The effect of the solvent polarity as well as the effect of the entropic contributions are also considered.
The rearrangement reaction of the volatile cyanotritylcarbenes is another topic. These carbenes readily rearrange to ethene main products, however also small amount of the unexpected heptafulvenes is formed. This unprecedented heptafulvene formation is modeled in detail and the energetics is systematically evaluated to identify most reasonable rearrangement pathways of the probable multiple alternative routes. Computational investigation of other tritylcarbenes with varying spectator substituents results in sophisticated data base for experimental investigations.
At last, some controversial observations in experimental studies concerning the kinetics of the electrophilic alkylation of the barbiturate anion are studied. To interpret the kinetic measurements, different alkylation pathways are analyzed with respect to their energetics. Further, the influence of microsolvation is demonstrated.
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Sejwal, Preeti. "I. Water-driven chemoselective reactions of squarate derivatives with amino acids and peptides Mechanism and applications. II. Biocompatible hydrogels: Transferring bioinert chemistry from surfaces to 3-dimensional materials /." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2008. http://wwwlib.umi.com/cr/syr/main.
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Cabrini, Liliane Girotto. "Aplicações das Tecnicas de Espectrometria de Massas e Ressonancia Magnetica Nuclear na Detecção e Caracterização de Intermediarios Chave de Reações Organicas." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/248682.
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Orientador: Marcos Nogueira EberlinDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
Made available in DSpace on 2018-08-08T11:34:29Z (GMT). No. of bitstreams: 1 Cabrini_LilianeGirotto_M.pdf: 4710376 bytes, checksum: d7e2a14030bf7b1a4a9e90a9a50031ad (MD5) Previous issue date: 2007
Resumo: Esta dissertação de mestrado e dividida em duas partes. A primeira parte, visa, através da técnica de RMN, detectar e estudar a reatividade dos íons N-acilimínios endo- e exocíclicos de 5 e 6 membros, com a finalidade de verificar se o tamanho do anel, a presença de anel aromático e se a diferença entre o grupo acila endo- ou exocíclicos afetam a estabilidade do íon N-acilimínio. Experimentos realizados com a N-carbometoxi-1-metoxi-tetraidroisoquinolina (38), em CDCl3, à - 30.°C e na presença de BF3.OEt2, mostrou a presença no espectro de RMN de H um sinal bastante intenso na região de d 9, referente ao hidrogênio metínico do íon N-acilimínio (H-1), bem como um sinal a d 171,1 no espectro de RMN de C referente ao C-1 característicos da formação do íon N-acilimínio. A segunda parte descreve experimentos desenvolvidos no laboratório Thomson de espectrometria de Massas, no estudo de diferenciação de isômeros através do aparelho Pentaquadrupolo e a determinação do mecanismo de olefinação de Takeda por Electrospray. A diferenciação de isômeros em espectrometria de massas sempre foi um grande desafio. No presente trabalho, através de reações íon-molécula no espectrômetro de massas pentaquadrupolar, íons acílios (acilpirrol e acilpiridina) reagiram com diferentes classes de compostos, como acetal cíclico, epóxido, nitrila e dieno. Como resultado destas reações íon-molecula foi possível detectar e diferenciar a classe de isômeros N-, 2- e 3-acilpirróis e 2-, 3- e 4-acilpirridinas. A preparação de olefinas altamente substituídas através da olefinação de carbonilas utilizando sistemas gem-dicloro- Cp2Ti[P(OEt)3]2 foram estudadas por Takeda, e o mecanismo desta reação foi por nos elucidado, onde pode-se observar a formação de intermediários titanoceno e do titanociclo
Abstract: This master's thesis is divided in two parts. The first one had the objective to investigate via the NMR technique the reactivity of endo- and exocyclic N-acyliminium ions of 5 and 6 member-rings as a function of ring size, the presence of an aromatic ring and endo or exocyclics acyl groups. For all substracts we observed a deshielding of all the signals in the H-NMR spectra in the presence of Lewis acid. This dishielding was attributed to formation of a Lewis complex. One of such substrates (38) displayed in the H-NMR spectrum an intense singlet at d 9 which was assigned to the methyne hydrogen of the corresponding N-acyliminium ion. This dishielding was also detectable in the C-NMR spectrum (d 171,1). The second part of this thesis describes mass spectrometric (MS) experiments applied in the differentiation of isomers via pentaquadrupole MS, and for the determination of the mechanism of Takeda's olefination via electrospray-MS (ESI/MS). Using ion/molecule reactions of acyl ions (acylpyrrol and acylpiridine) with molecules of different classes such as cyclical acetals, epoxides, nitriles and dienes, it was possible to distinguish the N -, 2- and 3-acylpyrrol and the 2 -, 3- and 4-acylpiridine isomers. The preparation of olefins highly substituted via the carbonyl olefination using gem-dicloro-Cp2Ti[P(OEt)3]2 had been studied by Takeda, and the present ESI-MS results provide insights into its mechanism via the characterization of titanocene and titanocycle intermediates
Mestrado
Quimica Organica
Mestre em Química
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Isin, Emre M. "Potential Prodrugs of the Neuronal Nitric Oxide Synthase and Monoamine Oxidase Inhibitor 7-Nitroindazole and Structurally Related Compounds." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/35829.
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Parkinson's disease (PD) is a progressive neurodegenerative disorder of unknown cause that afflicts about 1.5 million Americans. The characteristic feature of PD is a deficiency of dopamine in the terminals of nigrostriatal neurons. Two enzyme systems, the neuronal form of nitric oxide synthase (nNOS) and monoamine oxidase B (MAO-B), have been linked to neurodegenerative pathways leading to PD. Several MAO-B and nNOS inhibitors have been evaluated for their neuroprotective properties in the mouse model of neurodegeneration which employs the parkinsonian inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). One such compound is 7-nitroindazole (7-NI), a compound which is reported to inhibit both enzymes.
This thesis focuses on the synthesis and biological evaluation of a potential prodrug form of 7-NI and related indazolyl containing compounds which are designed to release the active drugs following a metabolic bioactivation process. These studies have led to a detailed description of the nucleophilic aromatic substitution reactions between 4-chloro-1-methylpyridinium iodide and the indazolyl reactants that were employed as the initial step in the synthesis of the target compounds. The MAO-B substrate and inhibition properties of these "prodrugs" as well as the parent indazolyl compounds were examined. The results are discussed in relation to a previously developed active site model of MAO-B.
Master of Science
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Phanasgaonkar, Alka 1956. "Diffusion and protection mechanisms of migratory corrosion inhibitors in reinforced concrete." Monash University, Dept. of Materials Engineering, 2000. http://arrow.monash.edu.au/hdl/1959.1/9200.
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Peck, Jamie. "A combined approach of electronic structure calculations and spectroscopy for elucidating reaction mechanisms in organic and bioinorganic systems." Thesis, University of East Anglia, 2012. https://ueaeprints.uea.ac.uk/42360/.
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This thesis describes the use of density functional theory (DFT) to assist the interpretation of advanced spectroscopic techniques such as stopped flow Fourier transform infrared spectroscopy (FTIR), muon spin resonance (�SR), and nuclear inelastic scattering (NIS). These complementary techniques are used to investigate the structure and mechanism of a variety of important chemical systems, some of which are relevant to biological energy transduction and energy harvesting. The mechanisms by which [FeFe] and [NiFe] hydrogenase enzymes catalyse the reversible reduction of protons to dihydrogen are of intrinsic interest in the context of a developing hydrogen technology for energy transduction. Gas phase DFT calculations are used to simulate and assign structure to experimental solution phase FTIR spectra for a family of [FeFe]-hydrogenase model complexes. Further, the Mulliken charge distribution across the Fe centres are compared for di�erent dithiolate bridge groups and PMe3 ligand positions. In the pursuit of understanding the protonation mechanism of [FeFe]-hydrogenases, transition state theory is used and the energetics of reaction pathways leading to terminal and bridging hydrides calculated and compared. NIS demonstrates great potential for characterising the [FeFe]-hydrogenase mimics. In order to further develop and validate the technique, a combination of NIS, DFT calculations, FTIR and Raman spectroscopies are applied to a small Fe(III) model system in order to provide complete a characterisation of the low frequency metal
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Keppler, Artur Franz. "Estudo de mecanismos de reações envolvendo compostos de telúrio e aplicações sintéticas de compostos calcogenados." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/46/46135/tde-03082009-164709/.
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Nesse trabalho foi apresentada a primeira evidência experimental da formação de radicais orgânicos centrados em telúrio (Rte• , onde R= grupos fenila ou butila) durante as reações de hidroteluração de alcenos e alcinos. Os radicais foram detectados por ressonância paramagnética eletrônica (EPR), usando como captador de spin o DBNBS (3,5-dibromo-4-nitrosobenzeno-sulfonato). Os adutos radicalares (DBNBS/•TeBu and DBNBS/•TePh) apresentaram um espectro de EPR caracterizado por um triplo tripleto, referente à um átomo de nitrogênio e dois de hidrogênio equivalentes ( e um valor de g de 2,0060. A presença do átomo de telúrio foi confirmada pela substituição isotópica (125Te) e por experimentos de espectrometria de massa. Os compostos detectados apresentaram padrões de distribuição isotópica esperados para compostos contendo átomos de Te e Br. Esses resultados forneceram evidências suficientes para provar que radicais orgânicos centrados em telúrio são formados e sugerir que as reações de hidroteluração ocorrem por uma mecanismo radicalar. O mecanismo das reações de adição de TeCI4 à alcinos foi indiretamente determinado pela detecção de radicais •TeCl3, usando as técnicas de EPR spin trapping em conjunto com a caracterização dessas espécies por ESI-MS and ESI-MS/MS. Radicais centrados em carbono foram detectados durante a reação sequencial Michael/Aldol induzida por butilcalcogenolatos de lítio. As reações de butilcalcogenolatos de lítio com alcenos ativados e aldeídos levaram aos correspondentes produtos aldólicos. Os selenetos sintetizados serviram como precursores de adutos de Baylis-Hillman após a reação de eliminação de selenóxido. Toda a sequencia reacional foi feita em metodologia one-pot.The first experimental evidence for the formation of an organic tellurium-centered radical (RTe center dot, R = Ph or nBu groups) during the hydrotelluration of alkenes and alkynes is provided. The radicals were detected by electronic paramagnetic ressonance (EPR), using DBNBS (3,5-dibromo-4-nitrosobenzene-sulfonate) as the spin trap. The radical adducts (DBNBS/TeBu and DBNBS/TePh) presented an EPR spectrum characterized by a triplet of triplets due to one nitrogen and two equivalent hydrogen atoms (aN = 21.6 G and aH = 0.7 G) and a g value of 2.0060. The presence of tellurium radical adducts was confirmed by isotopic substitution (125Te) and by electrospray and chemical ionization mass spectrometry and MS/MS analysis. The products showed isotopic patterns expected for compounds containing Br and Te. These results provide evidence for organic tellurium-centered radical formation and suggest that the hydrotelluration reactions occur by a free radical mechanism. The mechanism of the addition reaction of TeCl4 to alkynes was indirectly established by the detection of TeCl3 using EPR spin trapping, ESI-MS and ESI-MS/MS characterization. Carbon centered radicals were detected during the lithium butylchalcogenolate induced Michael-aldol tandem sequence. Reaction of the lithium alkylchalcogenolates with activated alkenes and aldehydes gives the corresponding aldol adducts. The selenium-containing products give MoritaBaylisHillman adducts after the oxidation/elimination of the selenoxide. The whole sequence can be performed in a one-pot procedure.
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Casellas, Soler Josep. "Elucidating deactivation and reaction paths of photosensitive organic systems through computational methods." Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/386574.
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Aquesta tesis estudia computacionalment els processos que expliquen les propietats fotoquímiques de certs compostos orgànics. Per això s’han fet servir mètodes ab initio multiconfiguracionals, CASSCF i CASPT2, amb els que es descriu la topografia de les superfícies d’energia potencial dels estats de més baixa energia i es localitzen els camins de reacció.
S’ha estudiat primerament el mecanisme de fotoisomerització del azobenzè i el seu derivat, la fenilazopiridina. El mecanisme de reacció obtingut explica satisfactòriament perquè el rendiment quàntic de la isomerització depèn de l’excitació inicial i del grau de restricció de la rotació interna en aquests sistemes. També s’ha analitzat un protocol computacional per la reproducció de l’espectre d’absorció en solució de sistemes flexibles, fent servir com a exemple la fenilazopiridina.
S’ha estudiat també la 9-fenilfenalenona. A diferencia del sistema del que deriva, la fenalenona que presenta un alt rendiment quàntic de sensitització de oxigen singlet, el rendiment quàntic de la 9-fenilfenalenona és molt baix. S’ha demostrat que aquest fet es deu a que en el segon compost la fotoexcitació produeix la formació d’un fotoproducte metaestable per ciclació que ràpidament reverteix al compost original. Aquest estudi ha suposat un repte pel mètodes computacionals que s’han fer servir per la seva gran mida.
Per últim s’ha estudiat el dehidroescualè, un carotenoide que intervé en processos d’absorció d’energia lumínica d’organisme vegetals. L’estudi determina l’estructura dels estats excitats de baixa energia i la influència de la flexibilitat d’aquest compost en les energies d’aquests estats. Es demostra que l’aproximació de fer servir tan sols la conformació més simètrica proporciona bons resultats a nivell qualitatiu però que, si es busca la reproducció quantitativa de les observacions experimentals, s’ha de tenir en conta la flexibilitat molecular.Esta tesis estudia computacionalmente los procesos que explican las propiedades fotoquímicas de ciertos compuestos orgánicos. Para ello se han usado métodos ab initio multiconfiguracionales, CASSCF y CASPT2, con los que se describe la topografía de las superficies de energía potencial de los estados de más baja energía y se localizan los caminos de reacción. Se ha estudiado primeramente el mecanismo de fotoisomerización del azobenzeno y su derivado, la fenilazopiridina. El mecanismo de reacción obtenido explica satisfactoriamente por qué el rendimiento cuántico de la isomerización depende de la excitación inicial y del grado de restricción de la rotación interna en estos sistemas. También se ha analizado un protocolo computacional para poder reproducir el espectro de absorción en disolución de sistemas flexibles, usando como ejemplo la fenilazopiridina. Se ha estudiado también la 9-fenilfenalenona. A diferencia del sistema del que deriva, la fenalenona, que presenta un alto rendimiento cuántico de sensitización de oxígeno singlete, el de la 9-fenilfenalenona es muy bajo. Se ha demostrado que eso se debe a que en el segundo la fotoexcitación produce la formación por ciclación de un fotoproducto metaestable que rápidamente revierte en el compuesto original. Este estudio ha supuesto un reto para los métodos computacionales empleados debido a su gran tamaño. Por último se ha estudiado el dehidroescualeno, un carotenoide que interviene en procesos de absorción de energía lumínica de organismos vegetales. El estudio determina la estructura de los estados excitados de baja energía y la influencia de la flexibilidad de este compuesto en las energías de estos estados. Se demuestra que la aproximación de utilizar sólo la conformación más simétrica proporciona buenos resultados a nivel cualitativo pero que, si se busca la reproducción cuantitativa de las observaciones experimentales, se debe tener en cuenta la flexibilidad molecular.
This thesis develops a computational work to study the processes that explain the photochemical properties of some organic compounds. Multiconfigurational ab initio methods, CASSCF and CASPT2 have been used to determine the topography of the potential energy surfaces of the low energy states and locate reaction paths. We have studied first the mechanism of photoisomerization of azobenzene and its derivative phenylazopyridine. The reaction mechanism obtained explains satisfactorily why the isomerization quantum yield depends on the initial excitation and on the degree of the restriction on the internal rotation of these systems. We have also analysed the performance of a computational protocol to reproduce the absorption spectrum of flexible systems in solution, using phenylazopyridine as target system. We have also studied 9-phenylphenalenone. Its parent system, phenalenone, shows a high quantum yield in the process of singlet oxygen sensitization, but the quantum yield of this phenyl derivate for the same process is very low. Our study shows that this difference is due to a side reaction induced by the initial photoexcitation, which produces a metastable photoproduct by cyclisation that turns back quickly to the initial reactant. This study has been a challenge for the computational methods used due to its big size. Finally, we have studied dehidrosqualene, a carotenoid involved in light harvesting processes in vegetables. Our study determines the structure of the low energy excited states and the influence of the flexibility of this compound in the energy of these states. We show that to use only the most symmetric conformation on this flexible compound to calculate the energy of the excited states, give results that qualitatively agree with the experimental observations but, if quantitative agreement is required, the molecular flexibility must be taken into account.
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Severin, Erik Jon. "Array-based vapor sensing using conductive carbon black-polymer composite thin film detectors : thesis /." Caltech Library System, electronic theses, 1999. http://etd.caltech.edu/etd/available/etd-12272004-162841/.
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Thesis (Ph.D.)--California Institute of Technology, 1999."UMI number: 9941121"--T.p. verso. Includes bibliographical references. Also available on microfilm. On-line version available via Caltech Library System.
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Chen, Nan. "Kinetics of the hydrodechlorination reaction of chlorinated compounds on palladium catalysts." Link to electronic thesis, 2003. http://www.wpi.edu/Pubs/ETD/Available/etd-0823103-161859.
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Valenrod, Yevgeny. "Development of solid phase-dynamic kinetic resolution for syntheses of N-substituted [alpha]-amino acids." Diss., Online access via UMI:, 2005.
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Brito, Tânia Cristina Chicre Alcântara de 1977. "Efeito da ativação local do receptor capa opióide no extravasamento plasmático e migração de neutrófilos na articulação temporomandibular de ratos." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/290585.
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Orientadores: Claudia Herrera Tambeli, Luana FisherTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: Na tentativa de diminuir os efeitos colaterais de ação central associados ao uso dos analgésicos opióides, algumas estratégias têm sido desenvolvidas para que eles atuem especialmente nos receptores opióides periféricos. Nesse contexto, os receptores capa opióides são de grande interesse, uma vez que, em contraste com outros receptores opióides, sua ativação não está associada com efeitos colaterais periféricos significativos. Estudo recente, realizado em nosso laboratório demonstrou que a ativação de receptores capa opióides localizados na região da articulação temporomandibular de ratos reduz significativamente a nocicepção induzida pela administração do agente inflamatório formalina nessa mesma articulação. No entanto, ainda não havia sido investigado até então, se a ativação de receptores capa opióides localizados na região da articulação temporomandibular de ratos também diminuía a inflamação induzida pela formalina nessa mesma articulação. Nesse contexto, o objetivo deste estudo foi investigar se a ativação de receptores capa opióides localizados na região da articulação temporomandibular de ratos diminui o extravasamento plasmático e a migração de neutrófilos induzidos pela administração de formalina na articulação temporomandibular de ratos. A intensidade do extravasamento plasmático foi determinada pela concentração do corante Azul de Evans extravasado no tecido articular e a intensidade de migração de neutrófilos pela avaliação da atividade da enzima mieloperoxidase. Para avaliar as diferenças significativas entre os grupos de extravasamento plasmático e migração de neutrófilos foi usado o teste one-way ANOVA seguido do teste de Tukey e o nível de significância estatística foi p <0,05.Os dados estão expressos em valores como média ± S.E.M. A co- administração de formalina a 1,5% e U50,488 (agonista seletivo de receptor capa opióide) (50?g) reduziu significativamente o extravasamento plasmático (Média± EPM: 23,42 ?g/g ± 4,88) de forma dose dependente e reversível quando comparado com os demais grupos de 1,5?g (46,60 ?g/g; ± 5,40) e 30?g (37,60 ?g/g ±3,64). Quando o U50,488 foi administrado na articulação temporomandibular contralateral a que recebeu formalina 1,5%, ele não afetou o extravasamento plasmático. A co- administração de formalina a 1,5% e U50,488 (1,5?g) reduziu significativamente a migração de neutrófilo (1,10 ?g/mg ± 0,20) de forma dose dependente quando comparado com os demais grupos de 0,3?g (3,23?g/mg ± 0,56) e 0,75?g (2,4323 ?g/mg ± 0,42). Quando o U50,488 foi administrado na articulação temporomandibular contralateral a que recebeu formalina 1,5%, ele não afetou a migração de neutrófilos induzidos pela formalina. Este efeito antiinflamatório foi revertido pela administração prévia, na articulação temporomandibular ipsilateral, mas não contralateral, do antagonista seletivo do receptor capa opióide nor-BNI (cloridrato de nor-Binaltorfimina, 200?g). Este estudo demonstrou que a ativação local de receptores capa opióides na região da articulação temporomandibular reduz significativamente dois parâmetros importantes da inflamação, que são o extravasamento plasmático e a migração de neutrófilos, de uma forma dose-dependente e antagonista reversível. Esse efeito antiinflamatório, em conjunto com o potente efeito antinociceptivo previamente observado desse agonista capa opióide, sugere que drogas que atuem sobre os receptores capa opióides periféricos são promissoras para o tratamento da dor e da inflamação nas articulações temporomandibulares e, provavelmente, para o tratamento de outras condições de dor articular que possua componente inflamatório
Abstract: In an attempt to decrease central side effects associated with the use of opioids, some strategies have been developed by targeting peripheral opioid receptors. In this context, kappa opioid receptors are of major interest, since, in contrast to other opioid receptors, their activation is not associated with potent peripheral side effects. We have recently demonstrated that local activation of kappa opioid receptors significantly decreases formalin-induced temporomandibular joint nociception, however, whether it also decreases temporomandibular joint inflammation is not known. To address this issue, we evaluated if the selective kappa opioid receptor agonist, U50,488 (trans-(1S,2S)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] enzeneacetamide hydrochloride hydrate), administered into the temporomandibular joint decreases formalin-induced plasma extravasation and neutrophil migration. The intensity of plasma extravasation was determined by measuring the concentration of Evan's blue dye extravasated in the articular tissue and the intensity of leukocyte migration was determined by measuring Myeloperoxidase activity also in the articular tissue. Data were analyzed by ANOVA and Tukey post hoc test (p?0.05) and the results are expressed as mean ± EPM. The co-administration of 1.5% formalin with the selective kappa opiod receptor agonist U50,488 at 50 ?g significantly reduced the plasma extravasation (Mean±EPM: 23.42 ?g/g ± 4.88) compared to the other groups receiving 1.5% formalin plus U50,488 at 1.5?g (46.60 ?g/g ± 5,40) and at 30?g (37.60 ?g/g ± 3.64). When applied on the contralateral temporomandibular joint, U50,488 had no effect on formalin-induced plasma extravasation. The co-administration of 1.5% formalin with U50,488 at 1.5?g significantly reduced formalin-induced neutrophil migration (1.10 ?g/mg ±0.20) compared to the other groups receiving 1.5% formalin plus U50,488 at 0.3?g (3.23?g/mg ± 0.56) and at 0.75?g (2.43 ?g/mg ± 0.42). When applied on the contralateral temporomandibular joint, U50,488 had no effect on formalin-induced neutrophil migration. The anti-inflammatory effect of U50,488 was blocked by the ipsilateral, but not contralateral administration of the selective kapa opioid receptor antagonist nor-BNI (Nor-Binaltorphimine dihydrochloride). This study demonstrates that local activation of kappa opioid receptors decreases two important parameters of temporomandibular joint inflammation, that is, plasma extravasation and neutrophil migration, in a dose-dependent and antagonist-reversible manner. This anti-inflammatory effect taken together with the previously demonstrated potent antinociceptive effect of U50,488, suggest that drugs targeting peripheral kappa opioid receptors are promising for the treatment of inflammatory temporomandibular joint pain and probably, other articular pain conditions with an inflammatory basis
Doutorado
Fisiologia Oral
Doutor em Odontologia
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Sanan, Toby T. "APPLICATION OF COMPUTATIONAL METHODS TO THE STUDY OF ORGANIC MACROMOLECULES AND BIOMOLECULES: STRUCTURE AND MECHANISTIC INSIGHTS IN LARGER CHEMICAL SYSTEMS." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1275484113.
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Hurley, Jeffrey S. "Phase transfer catalysis of deuterium exchange reactions : II kinetic and mechanistic studies of the thermal decomposition of glycolate and hedta in the presence of the sodium salts of hydroxide, nitrate, nitrite, aluminate and carbonate." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/30717.
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Vaz, Boniek Gontijo. "Perspectivas mecanisticas de reações organicas catalisadas por paladio : Heck, oxa-Heck e acoplamento de Buchwald-Hartwig por ESI-MS/MS." [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/248671.
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Orientador: Marcos Nogueira EberlinDissertação (mestrado)- Universidade Estadual de Campinas, Instituto de Quimica
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Resumo: A espectrometria de Massas por eletronspray (ESI-MS) tornou-se um método prático para o estudo de mecanismos reacionais em solução. Neste trabalho importantes reações catalisadas por paládio: reação de Heck-Mizoroki, oxa-Heck e o acoplamento de Buchwald-Hartwig foram monitoradas por ESI-MS visando interceptar espécies que comprovam as atuais propostas mecanísticas ou que abram caminho para novas propostas para estas reações. O monitoramento das reações foi realizado no modo off-line, acompanhamento da reação em intervalos pré-definidos de tempo, no qual alíquotas das soluções reacionais foram retiradas e diluídas em solventes apropriados e injetados por infusão direta no QTOF. Importantes intermediários reacionais destas reações foram interceptados por ESI-MS e caracterizados por ESI-MS/MS, o que possibilitou confirmar as espécies catalíticas responsáveis pela formação da ligação carbono-carbono na reação de Heck-Mizoroki, os principais intermediários para proposta mecanística desta reação e as atuais propostas da reação oxa-Heck e do acoplamento de Buchwald-Hartwig. No caso da reação oxa-Heck, os paladaciclos interceptados são os primeiros indícios experimentais para atual proposta mecanística desta interessante transformação
Abstract: Eletronspray ionization mass spectrometry (ESI-MS) has become a practical tool to study reaction mechanisms in solution. In this work important reactions catalyzed by palladium: Heck-Mizoroki reaction, oxa-Heck reaction and Buchwald-Hartwig coupling were monitored by ESI-MS to intercept transient intermediates that show the current mechanistic proposals or to open the way for new proposals for these reactions. These reaction was monitored in offline mode, whereas aliquots of the reaction solutions were withdrawn and diluted in appropriate solvents and injected by direct infusion at the Q-TOF in pre-defined intervals of time. Important intermediates from these reactions were intercepted by ESI-MS and characterized by its tandem version ESI-MS/MS, which allowed confirming the catalytic species responsible for the formation of carbon-carbon bond in the Heck-Mizoroki reaction, the main intermediaries mechanistic proposal from this reaction and the current proposals of oxa-Heck reaction and the Buchwald-Hartwig coupling. In oxa-Heck reaction, the intercepted palladacycles are the first experimental evidence for this current mechanistic proposal for this interesting transformation
Mestrado
Quimica Organica
Mestre em Química
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Haindl, Michael [Verfasser], Ruth M. [Akademischer Betreuer] Gschwind, Werner [Akademischer Betreuer] Kremer, and Sabine [Akademischer Betreuer] Amslinger. "NMR Spectroscopic Investigations on Small Organic Molecules: Catalyst Stabilities, Low-Abundance Conformers, Intermediates and Reaction Mechanisms / Michael Haindl ; Ruth M. Gschwind, Werner Kremer, Sabine Amslinger." Regensburg : Universitätsbibliothek Regensburg, 2016. http://d-nb.info/1131875737/34.
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Tchernook, Ivan [Verfasser], Joachim [Akademischer Betreuer] Friedrich, Joachim [Gutachter] Friedrich, and Werner A. [Gutachter] Goedel. "Strategies for Computational Investigation of Reaction Mechanisms in Organic and Polymer Chemistry Using Static Quantum Mechanics / Ivan Tchernook ; Gutachter: Joachim Friedrich, Werner A. Goedel ; Betreuer: Joachim Friedrich." Chemnitz : Universitätsbibliothek Chemnitz, 2016. http://d-nb.info/1213814871/34.
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Stadlmair, Lara Fabienne [Verfasser], Thomas [Akademischer Betreuer] Letzel, Jörg [Gutachter] Drewes, Thomas [Gutachter] Letzel, and Peter [Gutachter] Schröder. "Enzymatic Transformation of Trace Organic Chemicals : Characterization of Reaction Mechanisms using Mass Spectrometric Technologies / Lara Fabienne Stadlmair ; Gutachter: Jörg Drewes, Thomas Letzel, Peter Schröder ; Betreuer: Thomas Letzel." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1166315142/34.
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Berkner, Joachim Ernst. "Synthesis and characterization of new organic electrically conducting polymers : part II: Direct carboxylation of sulfolene : part III: Effect of water on PTC systems : part IV: Mechanism of Phase transfer catalytic N-alkylation reactions." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/30715.
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Zimmermann, Marc. "Oxygen reduction reaction mechanism on glassy carbon in aprotic organic solvents." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI044/document.
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Afin de mieux comprendre et de dépasser les limites actuelles des systèmes métal-air non-aqueux, le mécanisme de réduction de l’oxygène (ORR) a été étudié en présence de cation alcalins dans divers solvants aprotiques. Sur la base de caractérisations électrochimiques sur électrode statique et d’électrodes tournantes disque-anneau, un mécanisme unique a été proposé afin de rendre compte de l’ORR en présence de cations alcalins. De plus, les différences observées d’un solvant à l’autre ont été expliquées en termes de capacité du solvant à solvater à la fois le cation alcalin en présence et l’anion superoxyde, mais aussi à sa capacité à séparer les paires d’ions. Un modèle cinétique basé sur ce mécanisme a montré un excellent accord avec les résultats expérimentauxIn order to better understand and overcome the current limitations of non-aqueous metal-air batteries, the oxygen reduction reaction (ORR) mechanism has been studied in presence of different alkali metal cations in several aprotic solvents. Based on electrochemical characterizations on static electrode and rotating ring-disk electrode, a unique mechanism has been proposed to account for ORR in presence of alkali metal cations. It has been further showed that the differences observed from one solvent to another could be linked to the solvent’s ability to solvate both the alkali metal cation and the superoxide anion, as well as its capability to separate ion-pairs. A kinetic model based on this mechanism has shown very good agreement with experimental results