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Ribeiro, Joao Marcelo Lamim. "Kinetics and Reaction Mechanisms for Methylidyne Radical Reactions with Small Hydrocarbons." FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/3023.
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The chemical evolution with respect to time of complex macroscopic mixtures such as interstellar clouds and Titan’s atmosphere is governed via a mutual competition between thousands of simultaneous processes, including thousands of chemical reactions. Chemical kinetic modeling, which attempts to understand their macroscopic observables as well as their overall reaction mechanism through a detailed understanding of their microscopic reactions and processes, thus require thousands of rate coefficients and product distributions. At present, however, just a small fraction of these have been well-studied and measured; in addition, at the relevant low temperatures, such information becomes even more scarce. Due to the recent developments in both theoretical kinetics as well as in ab initio electronic structure calculations, it is now possible to predict accurate reaction rate coefficients and product distributions from first-principles at various temperatures, often in less time, than through the running of an experiment. Here, the results of a first principles theoretical investigation into both the reaction rate coefficients as well as the final product distributions for the reactions between the ground state CH radical (X2Π) and various C1-C3 hydrocarbons is presented; together, these constitute a set of reactions important to modeling efforts relevant to mixtures such as interstellar clouds and Titan’s atmosphere.
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Amyes, T. L. "Mechanisms of carboxyl-activated elimination reactions." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383698.
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Wenninger, Matthias. "Sensitizing mechanisms, reaction mechanisms and reactive intermediate states in photocatalytic reactions on time scales from femto- to microseconds." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-176226.
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The development of renewable energy sources depicts a constantly growing interdisciplinary research field. Beyond photovoltaics chemical photocatalysis plays a small role, but is gaining more and more importance. In photocatalysis, light serves as an energy source for the chemical conversion of certain molecules. However, not only the application of photocatalysis as energy source but also the utilization of photocatalysis in chemical synthesis has attracted a deep scien- tific interest. For the optimization of photocatalytic systems a fundamental understanding oft the underlying processes is more than essential. Thereby, transient absorption spectroscopy has proved to be a very useful tool. On the one hand, the operation of a setup for transient absorption spectroscopy and on the other hand the systematic data evaluation requires physical and mathe- matical skills whereas the results cannot be interpreted without deep chemical knowledge. With- in the framework of the present thesis the cooperation between the fields of organic chemistry and physics has turned out as a very productive cooperation. Sensitizing mechanisms, reaction mechanisms and reactive intermediate states in photocatalytic reactions on time scales from femto- to microseconds are the object of the present work.
The present thesis will prove that the analysis of measurement data on the basis of established standard methods, such as the fitting of a sum of exponential functions to the temporal evolution of the measured signal, often is not sufficient for a complete interpretation of the data. Only a data analysis precisely adapted to the problem can lead to a fundamental understanding of the underlying processes.
In the first part of the present thesis, the focus lies on light-induced intramolecular charge transfer processes. Marcus Theory, which depicts the theoretical background, will be briefly in- troduced. On the basis of a molecular donor-bridge-acceptor system it will be shown that the damping coefficient β is not sufficient to differ unambiguously between coherent tunneling and incoherent hopping mechanism.
Flavin-capped DNA hairpins serve as a model for the investigation of intramolecular charge transfer processes. After photo-excitation, flavin induces a hole which migrates through the DNA strand. It will be shown that an adapted base sequence allows for quantum yields of ΦCS = 14% for long-lived charge separated states.
In the next section it will be discussed if the building blocks of the DNA are adapted to serve as chiral backbone for enantioselective photocatalysis. The conformation-dependent charge- transfer dynamics in benzophenone-DNA dinucleotides will be put on solid ground with the help of Marcus Theory. It will be shown that these dinucleotides are generally not suited to serve as an inert backbone for every kind of photochemical reaction.
In the following section a true bimolecular photocatalytic reaction will be discussed. Flavin serves as photocatalyst for the conversion of an alcohol to the corresponding aldehyde. A pre- cisely adapted data analysis allows and exact quantification of the diffusion controlled reaction dynamics on the ps time scale. The understanding of the process allows optimizing the reaction conditions. The targeted utilization of triplet chemistry within this reaction can help to increase the quantum yield for product formation.
As photo-induced charge transfer processes have been intensively discussed, the focus in the second part of the thesis lies on the [2+2] photocycloaddition. As basis for the interpretation of subsequent measurements, the [2+2] photocycloaddition of substituted quinolones will be inves- tigated. The formation of the cyclobutane ring in which the quinolone triplet state plays the cen- tral role will be characterized and quantified on the time scale from ps to ns. Afterwards the [2+2] photocycloaddition of substituted quinolones will be initiated by a chiral xanthone-based photocatalyst. It will be shown that within this catalyst-substrate complex in which both constit- uents have a distance of only few Ångströms, new electronic properties appear. The photo- excitation of a new electronic state not only initiates the [2+2] photocycloaddition of the quino- lone but also depicts a new sensitizing mechanism, which has to the author’s best knowledge not been observed in photocatalysis of organic molecules. The quinolone triplet state does not appear in this mechanism. The question, if this mechanism can be transferred to other photocatalytic systems has to be answered within the framework of further studies.Die Erforschung nachhaltiger und ressourcenschonender Energiequellen bildet ein stetig wachsendes, interdisziplinäres Forschungsfeld. Neben der Photovoltaik, die inzwischen eine etablierte Energiequelle darstellt, ist die chemische Photokatalyse noch ein kleines, aber stets wachsendes Teilgebiet. In der Photokatalyse dient das einfallende Licht dazu, chemische Ver- bindungen umzuformen. Nicht nur die Anwendung der Photokatalyse für die Energiegewinnung, sondern auch der Einsatz in der chemischen Synthese stößt dabei auf wachsendes Interesse. Um photokatalytische Systeme zu optimieren ist ein fundamentales Verständnis der Prozesse erfor- derlich. Die transiente Absorptionsspektroskopie hat sich dabei als geeignetes Werkzeug erwie- sen. Der Betrieb eines Aufbaus zur Messung transienter Spektren auf verschiedenen Zeitskalen und die gezielte Datenauswertung erfordert fundiertes physikalisches und mathematisches Ver- ständnis, wohingegen die Interpretation der Ergebnisse nicht ohne chemisches Wissen erfolgen kann. Im Rahmen dieser Arbeit hat sich die Kooperation zwischen der organischen Chemie und der Physik als erfolgreiche Zusammenarbeit erwiesen. Gegenstand der vorliegenden Arbeit sind die Sensibilisierungsmechanismen, die Reaktionsmechanismen und die reaktiven Intermediate in photokatalytischer Reaktionen auf Zeitskalen von Femto- bis Mikrosekunden. Es wird gezeigt, dass die Auswertung von Datensätzen mit Standardmethoden, wie der Anpas- sung einer Summe von Exponentialfunktionen an die zeitliche Entwicklung des Signals oft nicht ausreichend ist, um die Messdaten hinreichend zu interpretieren. Erst eine der Problemstellung exakt angepasste Datenanalyse führt zum Verständnis der zugrundeliegenden Prozesse. Zunächst werden lichtinduzierte intramolekulare Ladungstransferprozesse behandelt. Die the- oretische Basis für die Beschreibung solcher Prozesse bildet die Marcus-Theorie, die kurz einge- führt wird. Anhand eines molekularen Donor-Bridge-Acceptor-Systems wird gezeigt, dass der exponentielle Dämpfungskoeffizient β oft ungeeignet ist um der Reaktion einen kohärenten Tun- nelprozess oder einen inkohärenten Transfermechanismus zuzuweisen. DNS-Haarnadelstrukturen, welche kovalent mit einem Flavin-Chromophor verbunden sind, dienen als Modellsystem für die Untersuchung intramolekularer Ladungstransferprozesse. Nach Anregung induziert Flavin eine Elektronenfehlstelle in dem benachbarten DNS-Strang, die den Strang entlangwandern kann. Es wird gezeigt, dass durch die geeignete Wahl der Basensequenz eine Quantenausbeute von ΦCS = 14 % für langlebige ladungsgetrennte Zustände erreicht wird. In einem weiteren Abschnitt wird untersucht, ob die Bausteine der DNS als chirale Umgebung für die enantioselektive Photokatalyse geeignet sind. Mit Hilfe einer auf der Marcus-Theorie basierenden Interpretation der Messergebnisse wird die konformationsabhängige Ladungstrans- ferdynamik in Benzophenon-DNS-Dinukleotiden beschrieben. Es wird gezeigt, dass die Dinuk- leotide nicht uneingeschränkt für die enantioselektive Photokatalyse geeignet sind. Schließlich wird eine echte bimolekuare photokatalytische Reaktion untersucht. Dabei wird mit Hilfe von Flavin ein Alkohol in ein Aldehyd umgesetzt. Mit einer angepassten Datenauswer- tung werden diffusive Prozesse auf der ps-Zeitskala genau quantifiziert. Die gewonnen Informa- tionen dienen dazu, die Reaktionsbedingungen zu optimieren um über einen Triplett- Reaktionsmechanismus höhere Quantenausbeuten zu erzielen. Nachdem photoinduzierte Ladungstransferprozesse ausgiebig diskutiert wurden, liegt der Fo- kus im zweiten Teil auf der [2+2] Photocycloaddition: Als Grundlage für die Interpretation spä- terer Messungen wird zunächst die [2+2] Photocykloaddition an substituierten Chinolonen unter- sucht. Die einzelnen Reaktionsschritte der Ringbildung werden auf der Zeitskala von ps bis ns quantifiziert und charakterisiert, wobei der Triplettzustand den zentralen Zustand bildet. An- schließend wird die [2+2] Photocycloaddition an substituierten Chinolonen durch einen chiralen, auf dem organischen Chromophor Xanthon basierenden Photokatalysator initiiert. Es wird ge- zeigt, dass innerhalb des Katalysator-Substrat-Komplexes, in dem beide Moleküle einen Abstand von wenigen Ångström haben, neue elektronische Eigenschaften auftreten. Die Anregung eines neuen Zustands initiiert nicht nur die [2+2] Photocycloaddition sondern stellt auch einen neuen Sensibilisierungsmechanismus dar, der bisher in photokatalytischen Reaktion organischer Mole- küle nicht beobachtet wurde. Der Triplettzustand des Chinolons tritt hierbei nicht mehr auf. Ob sich dieser Sensibilisierungsmechanismus auch auf andere Systeme übertragen lässt, muss durch weitere Arbeiten auf diesem Gebiet geklärt werden.
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Smith, Dean A. "The demonstration of electron-transfer reactions and their effect on model lignin condensation reactions under alkaline pulping conditions." Diss., Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/5700.
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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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Krug, John P. "The mechanisms of enone-alkene photocycloaddition reactions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq21299.pdf.
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Tam, Kin Yip. "Mechanisms of reactions at solid-liquid interfaces." Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:a7525194-433f-4bc8-914a-da452c5ffc77.
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+ and the rate constant is quantified for the first time. The aforementioned spectroelectrochemical channel cell was then adopted to scrutinise the reactive dyeing kinetics on a cotton fabric. Kinetic results showed that the dye adsorption to the fabric is controlled by a solid-liquid interfacial reaction which is first order with respect to the surface concentration of the dye. However, the rate of this process is governed by the availability of the reaction sites for adsorption of dye molecules onto the fabric surface. It was demonstrated that the presence of supporting electrolyte in high pH media, and mercerisation pretreatment of the fabric, are essential to increase the dye uptake rate. Ex situ AFM studies suggested that mercerisation leads to a disordered fibre surface which may be responsible for the enhanced dye absorption rate.
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Baxter, Nicholas James. "The mechanisms of reactions of #beta#-sultams." Thesis, University of Huddersfield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285584.
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Laverty, Genevieve Mary. "Kinetics and mechanisms of thermal reactions involving solids." Thesis, Queen's University Belfast, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336105.
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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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Jenzer, Herbert Kurt. "Molecular mechanisms and side reactions of thyroid hormone biosynthesis /." [S.l : s.n.], 1987. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Birrell, James Alexander. "The mechanisms of flavin site reactions in NADH:ubiquinone oxidoreductase." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607665.
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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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Gordon, S. Fraser. "Investigations into the chemical and cellular mechanisms of drug hypersensitivity." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269702.
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Wenninger, Matthias [Verfasser], and Eberhard [Akademischer Betreuer] Riedle. "Sensitizing mechanisms, reaction mechanisms and reactive intermediate states in photocatalytic reactions on time scales from femto- to microseconds / Matthias Wenninger. Betreuer: Eberhard Riedle." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2014. http://d-nb.info/1062492730/34.
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Cortés, José E. (José Enrique). "Kinetics and Mechanisms of Ligand Exchange Reactions of Chelate Complexes." Thesis, University of North Texas, 1989. https://digital.library.unt.edu/ark:/67531/metadc330827/.
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Certain ligand substitution reactions proceed to a complete displacement of the chelate ligand. Certain reactions proceed through a mechanism involving an initial fission of the tungsten-sulfur bond to afford a coordinatively-unsaturated intermediate which is rapidly attacked by chlorobenzene. The resulting solvated intermediate establishes an equilibrium which involves desolvation-solvation. Although main group organometallic chemistry has received a great deal of attention, this discussion will be centered in organotransition metal chemistry, in particular, metal carbonyls.
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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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Somerville, Rosemarie Janet. "Mechanisms of Ni-Catalysed C–O Functionalisation and Carboxylation Reactions." Doctoral thesis, Universitat Rovira i Virgili, 2020. http://hdl.handle.net/10803/670352.
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Comprendre els mecanismes de les transformacions catalítiques és extremadament important, ja que permet als químics millorar les reaccions reduint, per exemple, la càrrega de catalitzadors, impedir la formació de subproductes o obtenir coneixement fonamental sobre l'estructura i l'enllaç dels intermedis. L'objectiu d'aquesta tesi rau en les transformacions recentment desenvolupades de la funcionalització C-O catalitzada per Ni i en les reaccions d'acoblament reductor catalitzades en Ni. Si bé aquestes reaccions es veuen facilitades per les propietats favorables de Ni en comparació amb Pd, l’abast dels mecanismes possibles per a una reacció catalitzada en Ni és més ampli i es coneix menys informació sobre els seus mecanismes en comparació amb les transformacions catalitzades per Pd. Entre els reptes d’entendre les característiques mecàniques s’inclouen els intermediaris potencialment inestables, la necessitat de dades cinètiques fiables i l’analització de les nombroses propostes mecàniques que s’han presentat. En aquest treball es presenten tres instantànies mecàniques d’aquestes transformacions catalitzades en Ni. El primer és un ampli estudi mecanicista de la sililació C – O catalitzada per Ni d’èsters arils, on es reporten els primers complexos d’addició oxidativa de Ni i èsters d’arils amb fosfina monodentada. El segon és una investigació sobre un intermediari proposat en reaccions d'acoblament reductiu: un complex Ni (I)-alquil. Un exemple va ser aïllat i caracteritzat per la cristallografia de rajos X i EPR. De manera significativa, també es va probar la seva reactivitat d’inserció de CO2. El tercer projecte fa llum sobre el paper de Zn com més que un reductor en la carboxilació catalitzada al Ni de sals de arilsulfoni.Comprender los mecanismos de las transformaciones catalíticas es extremadamente importante ya que esto permite a los químicos a mejorar las reacciones, por ejemplo, reduciendo la carga del catalizador, evitando la formación de subproductos u obteniendo conocimiento fundamental sobre la estructura y la unión de los intermedios. El objetivo de esta tesis radica en las transformaciones desarrolladas recientemente de la funcionalización C-O catalizada por Ni y las reacciones de acoplamiento reductor catalizadas por Ni. Si bien estas reacciones se ven facilitadas por las propiedades favorables de Ni en comparación con Pd, el alcance de los posibles mecanismos para una reacción catalizada por Ni es más amplio y se conoce menos información sobre sus mecanismos en comparación con las transformaciones catalizadas por Pd. Los desafíos para comprender las características mecanicistas incluyen intermedios potencialmente inestables, la necesidad de datos cinéticos confiables y el análisis de las numerosas propuestas mecanicistas que se han presentado. En este trabajo, se presentan tres instantáneas mecanicistas de estas transformaciones catalizadas por Ni. El primero es un amplio estudio mecanicista de la sililación C-O catalizada por Ni de ésteres de arilo, donde se informan los primeros complejos de adición oxidativa de Ni y ésteres de arilo con una fosfina monodentada. El segundo es una investigación sobre un intermedio propuesto en las reacciones de acoplamiento reductor: un complejo de Ni (I) -alquilo. Un ejemplo fue aislado y caracterizado por EPR y cristalografía de rayos X. Significativamente, su reactividad de inserción de CO2 también fue probada. El tercer proyecto arroja luz sobre el papel de Zn como algo más que un reductor en la carboxilación catalizada por Ni de sales de arilsulfonio.a
Understanding the mechanisms of catalytic transformations is extremely important as this allows chemists to improve reactions by, for example, reducing catalyst loading, preventing the formation of by-products, or obtaining fundamental knowledge about the structure and bonding of intermediates. The focus of this thesis lies with the recently developed transformations of Ni-catalysed C–O functionalisation and Ni-catalysed reductive coupling reactions. Whilst these reactions are facilitated by the favourable properties of Ni compared to Pd, the scope of possible mechanisms for a Ni-catalysed reaction is broader and less information is known about their mechanisms compared to Pd-catalysed transformations. Challenges in understanding mechanistic features include potentially unstable intermediates, a need for reliable kinetic data, and parsing the many mechanistic proposals that have been put forward. In this work, three mechanistic snapshots of these Ni-catalysed transformations are presented. The first is a broad mechanistic study of the Ni-catalysed C–O silylation of aryl esters, where the first oxidative addition complexes of Ni and aryl esters with a monodentate phosphine are reported. The second is an investigation into a proposed intermediate in reductive coupling reactions – a Ni(I)-alkyl complex. One example was isolated and characterised by EPR and X-ray crystallography. Significantly, its CO2 insertion reactivity was also probed. The third project sheds light on the role of Zn as more than just a reductant in the Ni-catalysed carboxylation of arylsulfonium salts.
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Gunnarsson, Iva. "SLE : pathogenetic mechanisms in nephritis and sulphasalazine-induced lupus reactions /." Stockholm, 1999. http://diss.kib.ki.se/1999/91-628-3654-4/.
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Purser-Hallard, Beatrice. "Kinetics and mechanisms of solid-state phase transitions and reactions." Thesis, Open University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422026.
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Cochain, Benjamin, V. Magnien, Daniel R. Neuville, and Pascal Richet. "Diffusion in silicate melts: kinetics and mechanisms of redox reactions." Diffusion fundamentals 6 (2007) 77, S. 1, 2007. https://ul.qucosa.de/id/qucosa%3A14257.
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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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Rule, Krista Lynn. "The Mechanisms, Products, and Kinetics of Triclosan-Free Chlorine Reactions." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/42791.
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The kinetics, products, and reaction pathways of triclosan/free chlorine reactions were investigated for the pH range 3.5-11. Although pH dependent speciation occurs in both triclosan and free chlorine, only the reaction between HOCl and the phenolate-triclosan was found to play a significant role in the kinetics. The second order rate constant for the reaction between phenolate-triclosan and HOCl was found to be 5.40 (±1.82) à 103 M-1s-1. Three chlorinated triclosan intermediates were tentatively identified based on mass spectral analysis. Additionally, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and chloroform formed under excess free chlorine conditions. The majority of the chloroform formed during the reactions does not form via 2,4-dichlorophenol and 2,4,6-trichlorophenol oxidation. Therefore, the majority of chloroform is likely formed via the oxidation of triclosanâ s phenolic ring. Based on the identified products, a reaction pathway was proposed for the oxidation of triclosan in the presence of free chlorine.Master of Science
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Kotcharaksa, Komgrit. "The Mechanisms, Products, and Kinetic of Carbamazepine-Free Chlorine Reactions." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/36422.
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Carbamazepine (CBZ) is an antiepileptic drug widely detected in drinking water supplies and wastewater effluent. It has been previously found that CBZ is recalcitrant to biological removal processes. Therefore, active CBZ will be exposed to wastewater effluent disinfection processes, which for most treatment plants in the United States involves the addition of free chlorine. However, the chlorination mechanisms of CBZ have not been fully investigated and are currently poorly understood. Our experimental studies were conducted to examine the chlorination of CBZ under controlled conditions. The kinetics, products, and reactivity of CBZ/free chlorine reactions were investigated over the pH range of 5.5-10. Results show that free chlorine reacts with CBZ and the reactivity is pH dependent. Furthermore, the results indicate that temperature affects the reactivity of CBZ with free chlorine. The temperature experiment results were fitted with the Arrhenius equation. The calculated Ea and A values are 48.8 kJ/mol and 1.41x104 s-1, respectively. Four common intermediates were detected based on both UV and mass spectral analysis proposed structures were developed based on m/z from mass spectra.Master of Science
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Zhuang, Yipping. "Mechanisms of alkane reactions over platinum and tungsten carbide catalysts." Doctoral thesis, Universite Libre de Bruxelles, 1995. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212599.
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Fardost, Ashkan. "Palladium(II)-Catalyzed Heck Reactions : Domino Reactions, Decarboxylations, Mechanistic Studies & Continuous Flow Applications." Doctoral thesis, Uppsala universitet, Institutionen för läkemedelskemi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-242259.
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This thesis describes research efforts dedicated to the development of palladium(II)-catalyzed oxidative Heck and Heck/Suzuki domino reactions, and the applications of a new microwave heating technology, purpose-built for continuous flow in organic synthesis. Paper I describes the development of a ligand-modulated approach for attaching aryl groups to a chelating vinyl ether. By switching the ligand being used, selectivity for the arylation could be shifted to obtain three different outcomes: internal α- or terminal β-arylation, as well as a serendipitously discovered domino α,β-diarylation process. The latter was proposed to be an effect of para-benzoquinone, effectively acting as a stabilizing π-acidic ligand with the ability to suppress β-hydride elimination. Paper II explores the performance of a new microwave heating technology in combination with continuous flow. The novel nonresonant microwave applicator allowed rapid heating of common laboratory solvents and reaction mixtures above their boiling points with stable and reproducible temperature profiles. The technology was successfully applied to small-scale method development and subsequent scale-out of palladium-catalyzed reactions, heterocycle synthesis and classical organic transformations such as the Fischer indole synthesis. Paper III focuses on developing regioselective oxidative decarboxylative Heck reactions with electron-rich olefins. Successful internal α-arylations were achieved using various olefins and ortho-substituted aromatic acids. The mechanism was also studied by ESI-MS analysis. Key cationic organopalladium intermediates were identified, as well as an unexpected palladium(II)-complex which was isolated and characterized. Its experimentally deduced structure was in accordance with the lowest energy minimum found by DFT calculations. Preliminary findings suggested that the complex acts as a catalyst trap. Paper IV studies the mechanism of the reaction in Paper III by means of DFT calculations. Reductive elimination was identified as the rate-determining step when using a linear enamide as the olefin, due to its propensity to form low energy chelates. Its chelating properties also played a key role in the stability of the isolated palladium(II)-complex. The complex, which can act as a catalyst trap, was characterized by X-ray crystallography.
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Deary, Michael Edward. "Peroxide bleach activation: kinetics and mechanisms of some acyl transfer reactions." Thesis, Northumbria University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493973.
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Boakes, Gavin. "Kinetics and mechanisms of halogen reactions involved in atmospheric ozone depletion." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446700/.
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The purpose of this thesis is to address some of the uncertainties associated with the key gas phase reactions implicated in atmospheric ozone depletion. Laboratory studies, employing flash photolysis coupled with time resolved UV/visible absorption spectroscopy have been used to investigate the kinetics of several free radical reactions. The spectroscopy incorporated charge coupled device (CCD) technology which facilitated rapid time scale broad band data acquisition giving rise to unequivocal monitoring of multiple absorbing species. Classical or numerical models were used to simulate the experimental data by optimising kinetic parameters. The improvements in both the accuracy and the precision associated with the CCD studies have led to a profound improvement in our understanding of the roles of the free radical reactions studied in the Earth's atmosphere. The focus of the studies in this thesis was the reactions of halogenated species. These species are known to destroy atmospheric ozone through the reaction schemes such as: (1) XO + XO → 2X + O2 (2) X + O3 → XO + O2 Here, species X represents a halogen atom: Cl, Br or I, and this halogen atom is continously regenerated following flux through reactions (1) and (2) promoting further ozone destruction. The relatively high atmospheric abundance of ozone (typically parts per million in the lower stratosphere) compared to halogen atoms and free radicals (parts per trillion) ensures that reaction (1) is the rate determining step in the ozone depletion cycle. Consequently, a knowledge of the rate of reactions of type (1) under appropriate atmospheric conditions is fundamental in assessing the extent of halogen induced atmospheric ozone depletion. This thesis reports results from extensive investigations into three reactions of type (1) (i) BrO + BrO A study at 298 K and 760 Torr (ii) CIO + CIO A study over the ranges 206-320 K and 25-760 Torr, incorporating measurement of the differential CIO absorption cross section over this temperature range. (iii) BrO + CIO A study over the ranges 210-320 K and 100-760 Torr.
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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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Hanly, Ann Marie. "Mechanisms of reactions of N-arylsulfonyl derivatives of imines and oxaziridines." Thesis, University of Ulster, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260538.
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Gu, Xiaodong. "Oxidative lipid fragmentation; New mechanisms, synthesis and reactions of putative intermediates." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1275497811.
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Zapico, Alvarez David. "Mechanisms and kinetics of the galvannealing reactions on Ti IF steels." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2014. http://www.theses.fr/2014ECAP0019.
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Les revêtements galvanisés alliés sont produits par immersion à chaud d’une bande d'acier dans un bain de zinc fondu à environ 460 °C, saturé en fer et contenant de faibles quantités d'aluminium (de 0,1 à 0,135% poids), suivie d’un traitement thermique (jusqu'à des températures voisines de 500-530 °C pendant environ 10 s) afin de déclencher les réactions d'alliation entre le fer et le zinc. La microstructure finale de ce type de revêtement est composée d'une succession de couches stratifiées de phases Fe-Zn et ses propriétés d'usage sont directement liées à la distribution de ces phases dans le revêtement. Les paramètres process à appliquer sur ligne industrielle doivent donc être optimisés pour obtenir la microstructure de revêtement souhaitée avec des coûts minimaux. Le développement d'un tel revêtement passe par différentes réactions complexes : la formation de la couche d'inhibition, la rupture de cette couche, la consommation du zinc liquide et l'enrichissement en fer du revêtement solide. Les cinétiques de ces réactions doivent être étudiées et modélisées séparément afin de contrôler avec précision l'évolution du revêtement au cours du cycle thermique. Dans ce travail, les deux premières réactions ont été étudiées dans le cas des aciers IF Ti. La cinétique de formation de la couche d'inhibition est extrêmement rapide et n’a par conséquent pas été étudiée. L'attention a été portée sur la nature de cette couche et sur les mécanismes responsables de sa formation. Il a été démontré que la couche d'inhibition formée dans des bains classiques pour la production de ces revêtements est composée d'une première couche très mince de Fe2Al5Znx (20-30 nm) sur la surface de l’acier et d’une seconde couche plus épaisse de δ (FeZn7) (environ 200 nm) au-dessus. Lorsque l'acier est immergé dans le bain de zinc, la dissolution du premier dans le second conduit à une sursaturation en fer à l'interface solide / liquide. Une très fine couche de Fe2Al5Znx métastable germe alors sur la surface de l'acier favorisée par des relations préférentielles d’épitaxie avec la ferrite. Par la suite, une couche de δ germe sur la couche de Fe2Al5Znx ce qui permet à la microstructure finale de devenir thermodynamiquement stable. L'effet de la teneur en aluminium du bain sur la nature de la couche d'inhibition a également été étudié. Quand la teneur en aluminium du bain diminue, la couche de Fe2Al5Znx devient discontinue car cette phase devient plus métastable et sa germination sur la surface de l'acier moins probable. Cette étape d’inhibition n'est que transitoire et un traitement thermique prolongé conduira à la rupture de la couche d'inhibition et au développement des réactions Fe-Zn. Le mécanisme de rupture, contrôlé par la diffusion du zinc dans les joints de grains de l'acier, peut être expliqué à l'aide du diagramme de phase ternaire Al-Fe-Zn et résumé en deux étapes : la disparition de la couche de Fe2Al5Znx à l'interface couche d’inhibition / acier résultant de l’enrichissement de cette interface en zinc, et la germination de la phase Г (Fe3Zn10) aux joints de grains de l'acier lorsque la concentration en zinc y devient suffisante. C’est cette germination qui va provoquer localement la rupture de la couche d’inhibition. La cinétique de cette réaction dépend fortement de la composition chimique de l'acier IF Ti et de la teneur en aluminium du bain. D'une part, il apparaît que l'effet de la composition chimique de l'acier sur la cinétique de rupture d'inhibition est contrôlé par la compétition entre deux phénomènes opposés : la vitesse de diffusion du zinc dans les joints de grains de l'acier et la capacité de l'acier à y accumuler les atomes de zinc. D'autre part, la diminution de la teneur en aluminium du bain favorise la discontinuité de la couche de Fe2Al5Znx, ce qui accélère la rupture de la couche d'inhibition car le zinc est supposé diffuser plus rapidement dans δ que dans Fe2Al5ZnxHot-Dip GalvAnnealed (HDGA) coatings are produced by the immersion of the steel strip into an iron-saturated liquid zinc bath at around 460 °C containing small amounts of aluminium (from 0.1 to 0.135 wt.%, normally) and its subsequent heating (up to temperatures around 500-530 °C for about 10 s, typically) in order to trigger the alloying reactions between iron and zinc. The final microstructure of this kind of coatings is composed of a sequence of stratified Fe-Zn phase layers and its in-use properties are directly related to the phase distribution within the coating. The process parameters to be performed in industrial lines must therefore be optimized in order to obtain a successful coating microstructure with the minimum costs. The development of such a coating passes through different and complex reactions: the inhibition layer formation, the inhibition layer breakdown, the liquid zinc consumption and the iron enrichment of the solid coating. The kinetics accounting for these reactions must be studied and modelled separately in order to accurately control the evolution of the coating along the heat treatment performed in the industrial line. In the present work, the two first reactions were investigated in the case of Ti IF steel grades. The kinetics of the inhibition layer formation is extremely fast and has therefore not been investigated in detail. Concerning this reaction, the focus was given to the nature of this inhibition layer and to the mechanisms accounting for its formation. It has been found that the inhibition layer formed in typical baths for galvannealed coatings production is composed of a very thin layer of the Fe2Al5Znx phase (20-30 nm) on the steel surface and a thicker layer of the δ (FeZn7) phase (around 200 nm) on its top. As the steel strip enters the zinc bath, iron dissolution from the former into the latter leads to an iron supersaturation at the solid / liquid interface. As a result, a very thin layer of metastable Fe2Al5Znx nucleates on the steel surface favoured by preferential epitaxial relationships with ferrite. Subsequently, δ nucleates on the Fe2Al5Znx layer allowing the final microstructure of the inhibition layer to become thermodynamically stable. The effect of the bath aluminium content on the nature of this inhibiting structure has also been studied. As the bath aluminium content is lowered, the Fe2Al5Znx layer becomes discontinuous: the lower the bath aluminium content is, the higher the metastability of Fe2Al5Znx is and the less probable its nucleation on the steel surface is. The inhibition state is only transient and continued heat treatment will lead to the inhibition layer breakdown and the development of the further Fe-Zn alloying reactions. The breakdown mechanism, controlled by the diffusion of zinc towards the steel grain boundaries, can be explained using the Al-Fe-Zn ternary phase diagram and summarized in two steps: the disappearance of the Fe2Al5Znx layer at the inhibition layer / steel interface as a result of the enrichment of this interface in zinc, and the local nucleation of the Г (Fe3Zn10) phase at the steel grain boundaries, breaking the inhibition layer off, when the zinc concentration at these locations becomes high enough. The kinetics accounting for this reaction strongly depends on the Ti IF steel chemical composition and the bath aluminium content. On the one hand, it has been found that the effect of the steel chemical composition on the inhibition layer breakdown kinetics would be ruled by the competition between two opposite phenomena: the rate of zinc diffusion at the steel grain boundaries and the ability of the steel to accumulate the zinc atoms at these locations On the other hand, decreasing the bath aluminium content favours the discontinuity of Fe2Al5Znx, which accelerates the inhibition layer breakdown as zinc is expected to diffuse faster through δ than through Fe2Al5Znx
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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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Becker, Bruce. "Investigation of heavy ion reaction mechanisms by means of the inclusive 93Nb(12C,7Be) and 93Nb(12C,9Be) reactions." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/6993.
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Includes bibliographical references.Inclusive continuum cross-sections for the reactions 93Nb(12C,7Be) and 93Nb(12C,9Be) were measured at the NAC using a ΔE - E setup. A theoretical light output model which could account for the mass and charge dependance of the NaI E detectors was employed to calibrate the NaI(TI) detectors. The model is outlined and it is shown that the nonlinearity of the detector response is only due to a term which describes the mass-dependance. Investigation of the cross-sections revealed interesting facts about the dominant reaction mechanisms in the interaction of 120 with heavy targets. A theoretical model developed by the Milano group has been very successful in describing the continuum cross-sections of a particles (including 9Be) created in similar reactions of 120 and 160, incident on heavy targets. The analysis shows that the same description of the continuum cross-sections of 7Be and 9Be gives good agreement with the data (with different energy-loss parameters and survival probabilities), although there are discrepancies, especially at the lower incident angles. These small discrepancies may indicate the presence of a multistep direct reaction between the detected fragment and the residual nucleus in the exit channel. The most notable result of the analysis of the data was that the spectra of 7Be and 9Be, previously suspected to be created in a final-state interaction of sBe with the residual nucleus, are well-described by a friction-dissipative breakup mechanism.
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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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Gomez, David [Verfasser], and Stefan [Akademischer Betreuer] Klumpp. "Mechanisms of biochemical reactions within crowded environments / David Gomez ; Betreuer: Stefan Klumpp." Potsdam : Universität Potsdam, 2016. http://d-nb.info/1218400757/34.
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King, Martin D. "Kinetics and mechanisms of reactions of NOâ†3 with some biogenic species." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299017.
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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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Jones, John David. "The role of direct and indirect dynamical mechanisms in reactions at surfaces." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259624.
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Breno, Kerry L. "Organometallic catalysis in aqueous solution : reactions and mechanisms of water-soluble molybdocenes /." view abstract or download file of text, 2004. http://wwwlib.umi.com/cr/uoregon/fullcit?p3120612.
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Thesis (Ph. D.)--University of Oregon, 2004.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 213-252). Also available for download via the World Wide Web; free to University of Oregon users.
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Fuller, Jack Terrell. "Computational Studies on Mechanisms and Reactivity of Mercury and Cobalt Organometallic Reactions." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5974.
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Density Functional Theory (DFT) is a powerful tool for treating large organometallic structures efficiently and accurately. DFT calculations on the Hg-catalyzed oxidation of methane to methyl bisulfate in sulfuric acid suggest the lowest energy pathway involves a closed-shell electrophilic C–H activation mechanism coupled with metal alkyl reductive functionalization and oxidation by SO3. Comparison to Tl, Zn, and Cd suggests that Hg is unique in its ability to catalyze this set of reaction steps. Comparison to K2S2O8 highlights the selectivity of this C–H activation reaction as opposed to radical conditions. In contrast, DFT calculations indicate that CoIII(TFA)3 oxidizes methane through a radical TFA ligand decarboxylation pathway. A similar decarboxylation pathway is identified for MnIII(TFA)3, but the low spin ground state of TlIII(TFA)3 favors electrophilic C–H activation over this decarboxylation pathway. DFT calculations indicate that Cp(PPh2Me)Co=CF2 undergoes [2 + 2] cycloaddition with TFE by a unique open-shell singlet diradical mechanism. The significant stability of the perfluorometallacyclobutane reveals why catalytic metathesis with TFE is difficult.
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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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Green, Karen M. "Investigation of the mechanisms of chemiluminescent fluorine reactions of Manganese & Chromium /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486457871783155.
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Barradas, Gonçalo. "A Cross-Cultural Approach to Psychological Mechanisms Underlying Emotional Reactions to Music." Doctoral thesis, Uppsala universitet, Institutionen för psykologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-314870.
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Music plays a crucial role in everyday life by enabling listeners to seek individual emotional experiences. To explain why such emotions occur, we must understand the underlying process that mediates between surface-level features of the music and aroused emotions. This thesis aimed to investigate how musical emotions are mediated by psychological mechanisms from a cross-cultural perspective. Study I manipulated four mechanisms by selecting ecologically valid pieces of music that featured information relevant for each mechanism. The results suggested that listeners’ emotions could be successfully predicted based on theoretically based manipulations of target mechanisms. However, Study I featured only listeners from a single culture, neglecting the possible role of contextual and individual factors. Study II investigated the prevalence of emotions, mechanisms, and listening motives in a web survey featuring listeners from both individualist and collectivist countries. Results indicated that patterns of prevalence of emotions and mechanisms were quite similar across cultures. Still, Study II found that certain emotions such as nostalgia and the mechanism episodic memory were more frequent in collectivist cultures. In contrast, sadness and the mechanism musical expectancy were more frequent in individualist cultures. Study II also suggested that listening motives were country-specific, rather than subject to the individualism-collectivism dimension. Study III explored how particular mechanisms are manifested within a collectivist cultural setting with great potential for deeply felt emotions: fado music in Portugal. Interviews with listeners provided in-depth information on how the cultural context might shape listening motives and emotions. The results revealed that listeners strived for musical experiences that would arouse culturally valued emotions. Music-evoked nostalgia and contextual factors were regarded as important and contributed to an enhanced sense of wellbeing. Study IV tested the influence of lyrics on the emotions induced by Swedish and Portuguese pieces of music. The results revealed cross-cultural differences in how lyrics influenced emotions. The differences were not related to the music’s origin, but to the listener’s origin, suggesting that the impact of lyrics depends on the cultural background of the listener. In conclusion, the thesis suggests that cultural factors serve as moderators of effects of biologically based mechanisms for emotion induction.
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Jiménez, Halla José Óscar Carlos. "Theoretical study of catalytic reactions of carbenes: haptotropic rearrangements and the Dötz reaction." Doctoral thesis, Universitat de Girona, 2009. http://hdl.handle.net/10803/7942.
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En aquesta tesi s'han estudiat mecanismes de reaccions de cicloanulació en carbens de Fischer a través de mètodes teòrics, concretament fent servir el nivell de teoria B3LYP/(Wachters' basis / 6-31G**). Els alcoxi- i amino carbens de pentacarbonil crom, ja siguin vinílics o aromàtics, reaccionen amb acetilè per produir fenols, naftols o derivats ciclopentadiè o indè substituïts amb el Cr(CO)3 coordinat, d'una manera regioselectiva. L'objectiu d'aquest treball és discutir ambudes reaccions competitives particularment a la reacció de Dötz, la qual durant els darrers anys ha estat explorada experimentalment per W.D. Wulff, C.P. Casey, R. Aumann i J. Barluenga entre altres diferents propostes mecanístiques. A més K.H. Dötz va demostrar que la coordinació del Cr(CO)3, un cop l'anell ja està format, pot patir canvis haptotròpics, és a dir, la caminada del complex metàl·lic d'un anell a un altre -generalment almenys substituït- canviant la seva hapticitat (coordinació pi amb els membres de l'anell). Llavors, s'han estudiat les migracions haptotròpiques intramoleculars en petits hidrocarbons aromàtics policíclics amb l'objectiu d'analitzar les rutes de reacció per les quals aquestes reaccions es porten a terme
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Ladogana, Santino. "Kinetics and Mechanisms of Metal Carbonyls." Thesis, University of North Texas, 1998. https://digital.library.unt.edu/ark:/67531/metadc278709/.
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Pulsed laser flash photolysis with both visible and infrared detection has been applied to the study of the displacement of weakly coordinating ligands (Lw) by strongly "trapping" nucleophiles (Ls) containing either an olefinic functionality (Ls = 1-hexene, 1-decene, 1-tetradecene) or nitrogen (Ls = acetonitrile, hydrocinnamonitrile) from the photogenerated 16 electron pentacarbonylchromium (0) intermediate. 5-Chloropent-l-ene (Cl-ol), a potentially bidentate ligand, has been shown to form (ol-Cl) pentacarbonylchromium (0), in which Cl-ol is bonded to Cr via a lone pair on the chlorine, and isomerize to (Cl-ol) pentacarbonylchromium (0), in which Cl-ol is bonded to the olefinic functionality
on the submillisecond time scale. This process has been studied in both the infrared and visible region employing both fluorobenzene or n-heptane as the "inert" diluent. Parallel studies employing 1-chlorobutane and 1-hexene were also evaluated and showed great similiarity with the Cl-ol system. The data supported a largely dissociative process with a possibility of a small interchange process involving the H's on the alkyl chain. Studies were also carried out for various Cr(CO)6/arene/Ls systems (arene = various alkyl or halogenated substituted benzenes). The data indicated that for both C6H5R (R=various
alkyl chains) or multi-alkyl substituted arenes (i.e. o-xylene, 1,2,3-trimethylbenzene) containing an "unhindered" ring-edge, bonding to the the Cr(CO)5 moiety occurs "edge on" via a partially delocalized center of unsaturation on the ring. The data indicated that both electronic and steric properties of the arenes influence the kinetics, and that an interchange pathway takes place at least, in part, through the alkyl chains on both the arenes and "trapping" nucleophiles. Moreover, halogenated arenes bond through the lone pair on the halogen for both CI- and Br- derivatives but "edge-on" for the fluorinated arenes. Finally, in the case of arene complexes without and "unhindered" ring-edge (i.e.,
1,2,3,4,5-pentamethylbenzene) bonding can occur either "edge-on" or through the ring center of the arene or combination of the two. Carbonyl stretching frequencies for the arenes are also indicative of the type of bonding.
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Williams, Robert Earl Jr. "Simulation and Characterization of Cathode Reactions in Solid Oxide Fuel Cells." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16309.
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In this study, we have developed a dense La0.85Sr0.15MnO3-δ (LSM) Ce0.9Gd0.1O1.95 (GDC) composite electrode system for studying the surface modification of cathodes. The LSM and GDC grains in the composite were well defined and distinguished using energy dispersive x-ray (EDX) analysis. The specific three-phase boundary (TPB) length per unit electrode surface area was systematically controlled by adjusting the LSM to GDC volume ratio of the composite from 40% up to 70%. The TPB length for each tested sample was determined through stereological techniques and used to correlate the cell performance and degradation with the specific TPB length per unit surface area.
An overlapping spheres percolation model was developed to estimate the activity of the TPB lines on the surface of the dense composite electrodes developed. The model suggested that the majority of the TPB lines would be active and the length of those lines maximized if the volume percent of the electrolyte material was kept in the range of 47 57%. Additionally, other insights into the processing conditions to maximize the amount of active TPB length were garnered from both the stereology calculations and the percolation simulations.
Steady-state current voltage measurements as well as electrochemical impedance measurements on numerous samples under various environmental conditions were completed. The apparent activation energy for the reduction reaction was found to lie somewhere between 31 kJ/mol and 41 kJ/mol depending upon the experimental conditions. The exchange current density was found to vary with the partial pressure of oxygen differently over two separate regions. At relatively low partial pressures, i0 had an approximately dependence and at relatively high partial pressures, i0 had an approximately dependence. This led to the conclusion that a change in the rate limiting step occurs over this range.
A method for deriving the electrochemical properties from proposed reaction mechanisms was also presented. State-space modeling was used as it is a robust approach to addressing these particular types of problems due to its relative ease of implementation and ability to efficiently handle large systems of differential algebraic equations. This method combined theoretical development with experimental results obtained previously to predict the electrochemical performance data. The simulations agreed well the experimental data and allowed for testing of operating conditions not easily reproducible in the lab (e.g. precise control and differentiation of low oxygen partial pressures).
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Ali, Fawzia Runa. "Mechanisms of Late Asthmatic Reactions Induced By Inhalation of T Cell Peptide Epitopes." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498866.
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Allgäuer, Dominik. "Kinetics and mechanisms of the reactions of nitrogen ylides with acceptor-substituted olefins." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-181637.
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Ji, Yongfei. "Theoretical Studies on the Molecular Mechanisms of Photo-Catalytic Reactions on TiO2 Surfaces." Doctoral thesis, KTH, Teoretisk kemi och biologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145146.
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Photocatalysis is a promising technology that can effectively convert the solar energyinto sustainable green energy. However, theoretical studies on the molecular mechanisms of photocatalytic reactions are rare. This thesis is devoted to investigate several typical photocatalytic reactions on the surfaces of the most popular photocatalysis TiO2 with density functional theory. We start our study with the characterization of both the free and trapped hole on the surface generated by the light. The oxidation of physisorbed H2O molecule by the hole trapped at bridge oxygen on rutile TiO2(110) surface has been studied. The hole is found to transferto the molecule via the anti-bonding orbital as a result of the hybridization between the hole orbital and the HOMO of the molecule. The energy and symmetry mismatching between the trapped hole orbital and the HOMO of the molecule explains why the trapped hole cannot directly transfer to the chemisorbed H2O molecule. On the other hand, we have found that the chemisorbed H2O moleculecan be more efficiently oxidized by the free hole with a lower barrier and higher reaction energy compared to the oxidation by the trapped hole. In this reaction, the free hole is transferred to the chemisorbed H2O after the dissociation. This is different from the oxidation of chemisorbed H2O on anatase TiO2(101) surface by free hole, in which the hole is transferred concertedly with the dissociation of themolecule. In order to understand the hole scavenger ability of organic molecules, the oxidation of three small organic molecules (CH3OH, HCOOH and HCOH) onanatase TiO2(101) surface has been systematically investigated. The concerted hole and proton transfer is found for all these molecules. The calculations suggestthat both kinetic and thermodynamic effects need to be considered to correctly describe the hole transfer process. The order of hole scavenging power is found tofollow: HCOH > HCOOH > CH3OH > H2O, which agrees well with experiments. Photo-selective catalytic reduction of the NO by NH3 and the photooxidationof CO by O2 are closely related to the environment application. Both reactionsinvolve the formation and/or breaking of non R–H bonds. The mechanism for the photoreduction of NO proposed by experiment has been verified by our calculations.The role of the hole is to oxidize the adsorbed NH3 into ·NH2 radical, which canform a NH2NO complex with a gaseous NO molecule easily. The photooxidation of CO by O2 is the first multi-step photoreaction we ever studied. By combining thepotential energy surfaces at the ground and excited state we have found that thehole and electron both take part in the reaction. A molecular mechanism which is in consistent with various experiments is proposed. These studies show that density functional theory is a powerful tool for studying the photocatalytic reaction. Apparently, more work needs to be done in orderto improve the performance of the existing materials and to design new ones thatcan take advantage of the solar light more efficientlyQC 20140522