Dissertations / Theses on the topic 'Free radical reactions'
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1
Barreto, Joao Pedro Cabaco Moniz. "Dioxygen free radical reactions." Thesis, Oxford Brookes University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389105.
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Euapermkiati, Anucha. "Free radical telomerisation reactions." Thesis, University of Bradford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278895.
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Hancock-Chen, Tanya. "Biologically relevant free radical reactions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0019/NQ58282.pdf.
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Singh, Rajinder. "Free radical ring expansion reactions." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293427.
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Zhao, Zhijun. "Laser flash photolysis studies of some gas phase reactions of atmospheric interest." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31790.
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Thesis (Ph.D)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2010.Committee Chair: Wine, Paul; Committee Member: Huey, Greg; Committee Member: Mulholland, James; Committee Member: Nenes, Athanasios; Committee Member: Weber, Rodney. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Swann, Elizabeth. "An investigation of new free radical reactions." Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232882.
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Huther, Nathalie. "Novel manganese carbonyl-mediated free radical reactions." Thesis, University of York, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403967.
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Annis, Michael Colin. "Free radical cascade reactions involving furan rings." Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394991.
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9
Wood, Geoffrey Paul Farra. "Theoretical Investigations of Radical-Mediated Protein Oxidation." Thesis, The University of Sydney, 2006. http://hdl.handle.net/2123/1413.
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This thesis primarily details the application of high-level ab initio quantum chemistry techniques in order to understand aspects of free-radical mediated protein oxidation. Traditionally, product analysis and electron paramagnetic resonance (EPR) spectroscopy are the primary means for elucidating the chemistry of protein oxidation. However, in experiments involving relatively small proteins reacting with a controlled radical-flux, a vast array of compounds can be produced, which are often difficult to analyse. Quantum chemical techniques on the other hand, can calculate the properties of any particular species directly, without suffering from the problems associated with experiment, such as side-reactions and chain processes. The results presented in this thesis are aimed at elucidating mechanistic details of protein oxidation, which might otherwise be difficult to probe experimentally. Chapter 1 gives an overview of the free-radical hypothesis of disease and ageing. Protein-derived radicals can undergo a variety of reactions, with the particular reaction that occurs depending on numerous aspects. Many types of reactions have been identified through radiolysis experiments of amino acids, and these are detailed in this chapter. In addition, the key reactive species are characterized and their different chemistries explained. Chapter 2 details the theoretical tools used throughout this thesis. Species with unpaired electrons (radicals) present unique problems for quantum chemistry to handle, thus an appropriate choice of theoretical technique is needed. The approach taken in this thesis is to use high-level compound methods, many of which have been directly formulated to give improved results for radical species, to provide benchmark quality results by which other less demanding techniques can be assessed. During the course of this study, it became apparent there was a void in the armoury of tools that could be used for the theoretical chemistry calculations. Chapter 3 details the formulation of a new tool in an attempt to fill this gap. Historically, the formulation of this new procedure came after much of the work in this thesis had been carried out. Thus, for the study of many of the reactions of this thesis the new method has not been used. However, it is most appropriate to place its formulation after summarizing the current status of techniques in common use today. Chapters 4 and 5 detail computations carried out on models of peptides containing backbone carbon- and nitrogen-centered radicals. A number of different theoretical techniques are used in these chapters, ranging from the highly accurate and computationally intensive to the less reliable and less demanding. The highly accurate techniques are used to gauge the accuracy of the other less demanding theoretical techniques so that the latter can be used with confidence in larger systems. Not only is the choice of theoretical technique important but also the judicious choice of model is essential. With this in mind, models are incrementally built until convergence of the particular property of interest is reached. Chapters 6 and 7 detail the calculations of β-scission reactions of alkoxyl radicals, which are a particular class of reaction known to occur on peptide backbones. Alkoxyl radicals are particularly difficult for theory to describe correctly. Therefore, Chapter 6 extensively assesses and then identifies the theoretical methods needed to portray them. Chapter 7 uses the techniques identified in the previous chapter in order to predict how the preference for a particular type of β-scission reaction changes.
10
Wood, Geoffrey Paul Farra. "Theoretical Investigations of Radical-Mediated Protein Oxidation." University of Sydney, 2006. http://hdl.handle.net/2123/1413.
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Doctor of Philosophy (PhD)This thesis primarily details the application of high-level ab initio quantum chemistry techniques in order to understand aspects of free-radical mediated protein oxidation. Traditionally, product analysis and electron paramagnetic resonance (EPR) spectroscopy are the primary means for elucidating the chemistry of protein oxidation. However, in experiments involving relatively small proteins reacting with a controlled radical-flux, a vast array of compounds can be produced, which are often difficult to analyse. Quantum chemical techniques on the other hand, can calculate the properties of any particular species directly, without suffering from the problems associated with experiment, such as side-reactions and chain processes. The results presented in this thesis are aimed at elucidating mechanistic details of protein oxidation, which might otherwise be difficult to probe experimentally. Chapter 1 gives an overview of the free-radical hypothesis of disease and ageing. Protein-derived radicals can undergo a variety of reactions, with the particular reaction that occurs depending on numerous aspects. Many types of reactions have been identified through radiolysis experiments of amino acids, and these are detailed in this chapter. In addition, the key reactive species are characterized and their different chemistries explained. Chapter 2 details the theoretical tools used throughout this thesis. Species with unpaired electrons (radicals) present unique problems for quantum chemistry to handle, thus an appropriate choice of theoretical technique is needed. The approach taken in this thesis is to use high-level compound methods, many of which have been directly formulated to give improved results for radical species, to provide benchmark quality results by which other less demanding techniques can be assessed. During the course of this study, it became apparent there was a void in the armoury of tools that could be used for the theoretical chemistry calculations. Chapter 3 details the formulation of a new tool in an attempt to fill this gap. Historically, the formulation of this new procedure came after much of the work in this thesis had been carried out. Thus, for the study of many of the reactions of this thesis the new method has not been used. However, it is most appropriate to place its formulation after summarizing the current status of techniques in common use today. Chapters 4 and 5 detail computations carried out on models of peptides containing backbone carbon- and nitrogen-centered radicals. A number of different theoretical techniques are used in these chapters, ranging from the highly accurate and computationally intensive to the less reliable and less demanding. The highly accurate techniques are used to gauge the accuracy of the other less demanding theoretical techniques so that the latter can be used with confidence in larger systems. Not only is the choice of theoretical technique important but also the judicious choice of model is essential. With this in mind, models are incrementally built until convergence of the particular property of interest is reached. Chapters 6 and 7 detail the calculations of β-scission reactions of alkoxyl radicals, which are a particular class of reaction known to occur on peptide backbones. Alkoxyl radicals are particularly difficult for theory to describe correctly. Therefore, Chapter 6 extensively assesses and then identifies the theoretical methods needed to portray them. Chapter 7 uses the techniques identified in the previous chapter in order to predict how the preference for a particular type of β-scission reaction changes.
11
Bebbington, Magnus W. P. "Nitrogen-directed free radical rearrangements." Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:316d2379-4019-4361-937d-ff1e064f8bb9.
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This thesis describes efforts to develop new methods for the synthesis of bridged azacycles using nitrogen-directed free radical rearrangements. Free radical addition to 7-azanorbornadienes were carried out to give 7-substituted 2- azanorbornenes (Scheme a.l, X-Y = RS-H or PhSe-H). [illustration in text ...] Scheme a. 1 Nitrogen-directed homoallylic radical rearrangement via intermolecular radical addition. A conceptually novel and theoretically interesting nitrogen-directed neophyl rearrangement (Scheme a.2) was developed into a synthesis of 2- azabenzonorbornanes 2. [illustration in text ...] Scheme a.2 Nitrogen-directed neophyl-like rearrangement to 2-azabenzonorbornanes. In this case the radical 1 was generated by Barton deoxygenation of 7- azabenzonorbornanols. The effect on rearrangement of bicyclic core substitution and of aromatic ring electronics was probed in some detail, and the process was synthetically useful for a wide range of substrates. Variation of the protecting group on nitrogen was investigated and the product profiles from neophyl-like rearrangement were consistent with a process driven by the stability of a radical α to nitrogen as a result of SOMO-lone pair orbital interaction. The kinetics and mechanism of these processes are examined where appropriate, leading to estimates of rate constants for the rearrangements.
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Sacripante, Guerino. "Radical reactions in organic synthesis." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75340.
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The 4-substituted glutarimide required for the synthesis of sesbanimide (53) was obtained by free radical addition of iodoacetamide onto the $ alpha, beta$-unsaturated ester (81) mediated by tributyltin; the lactol ring C was prepared by the analogous free radical cyclization of the $ alpha$-bromo-dipropargyl ketal 73.The syntheses of tricyclic carbapenems involved appropriately substituted monocyclic azetidinone precursors. Free radical 5- exo cyclizations led to the relatively unstable benzo carbapenems 116, 119 and 120. The 6- exo mode, however, afforded stable benzo carbacephems 125, 127, 132 and 133.
$ alpha$-Bromo- and $ alpha{,} alpha$-dibromoazetidinones were converted stereoselectively to the $ alpha$-alkylazetidinones 149 and 153, or to $ beta$-alkylazetidinones 151, 154 and 159 by a free radical addition onto olefins 148 or allyltributyltin.
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Ishaq, Ahtsham. "The development and use of novel green radical methodology." Thesis, University of Aberdeen, 2010. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=158370.
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Over the last forty years the steady use of radical reactions as the key steps in syntheses has increased. The most commonly used radical reagent is tributyl tinhydride. However such tin based radical reagents are toxic and often contaminate the product as they are difficult to remove. As an alternative to these tin reagents, a novel NaBH4/U.V. system was developed. This system was successfully used to effect the radical reduction of various aromatic halides. In light of these results it was thought that other useful transformations such as C-C bond formation could be achieved. Radical cyclisation onto unsaturated bonds, halogen atom transfers radical cyclisation (HATRC) and 1-5 hydrogen atom translocations were explored. This, 1-5 hydrogen atom translocations, methodology has been successfully applied to the synthesis of the spirocyclic natural products (±) horsfiline and coerulescine. With this success the use of the NaBH4/U.V. system on pyridine substrates was explored. Unfortunately this was not achieved with our current understanding of this reaction. However the use of tributylgernamium hydride, which is considered a ‘green’ radical reagent when compared to tin based reagents, proved successful. The novel application of this reagent in the 1-5 hydrogen atom transfer reaction on pyridine substrates was successfully demonstrated. Its use was successfully employed in the synthesis of a pyridine based bioisostere derivative of horsfiline.
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Olivarès, Christel M. "Polyfluorinated systems resulting from free radical addition reactions." Thesis, Durham University, 2001. http://etheses.dur.ac.uk/3861/.
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The first part of this work was to synthesise partially fluorinated reactive compounds and then to study their reactivity towards nucleophiles and electrophiles. These reactive compounds were obtained in a two step process from both cyclopentane and adamantane and in a three step process for cyclopentanol. The first step was the free radical addition of the cycloalkanes, cycloalcohol to hexafluoropropene via thermal and/or radiochemical alkylations. For the cyclic alkane derivatives, the second step was a stereospecific dehydrofluorination of the fluorocarbon chain, whereas for the cyclic alcohol, a dehydration and then dehydrofluorination were performed to give the conjugated diene. Finally, the fluoroalkene reactivity was studied via nucleophilic and electrophilic addition reactions. The second part of my work was to study the free radical addition of tertiary amines to hexafluoropropene, an example is illustrated below.
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顧深 and Shen Gu. "Studies on Lewis acid-promoted radical cyclization reactions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243083.
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Gu, Shen. "Studies on Lewis acid-promoted radical cyclization reactions /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B24729735.
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Wang, Aileen Ruiling Zhu Shiping. "Diffusion-controlled atom transfer radical polymerization." *McMaster only, 2005.
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Seely, Franklin Lee. "Bis(trimethylstannyl)benzopinacolate Promoted Radical Carbon-Carbon Bond Forming Reactions and Related Studies." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1290711413.
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Smith, M. J. C. "Flash photolysis studies of gas phase free radical reactions." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355811.
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Myint, Pe. "Free radical reactions of hyaluronic acid in aqueous solution." Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292943.
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Ding, Shijie. "Atom transfer radical polymerization." Laramie, Wyo. : University of Wyoming, 2006. http://proquest.umi.com/pqdweb?did=1225138911&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Hutchison, Helen Susan. "Gas phase cyclisation and rearrangement reactions of aromatic free radicals." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/15081.
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Corser, David Alan. "Novel enzyme- and free radical-mediated reactions of oxirane derivatives." Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/27040.
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The thesis describes the use of various hydrolases in the preparation of enantiomerically enriched epoxyesters. Optically enriched n-butyl 4,5- epoxypentanoate was prepared with a 64% enantiomeric excess via the porcine pancreatic lipase-catalysed hydrolysis of the racemic ester. The hydrolase-catalysed hydrolysis of two prochiral epoxydiesters; meso 2,3-epoxybutan-1 A-diyl dibutanoate and 2,3-epoxy-2-butanoyloxymethylpropan-1-yl butanoate, were performed with several lipases, with the enantiomerically enriched epoxymonoesters being obtained in up to 80% and 65% enantiomeric excesses, respectively. Both isomers of the 4-butanoyloxy-2,3-epoxybutan-1-01 could be obtained via the hydrolysis of the diester by varying the lipase used. (2S, 3R)-4- Butanoyloxy-2,3-epoxybutan-1-01 was also isolated in up to 55% enantiomeric excess by the lipase-catalysed transesterification of vinyl butyrate with meso 2,3- epoxybutan-1 A-diol.
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Cai, Yudong. "Synthetic and mechanistic aspects of free-radical reactions in solution." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322240.
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Sharpe, D. J. "Applications of novel metal-free radical reactions in organic systems." Thesis, University of York, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425469.
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Farren, Christopher. "Polyfluorinated compounds via free-radical reactions of alcohols and diols." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4791/.
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Site-selective incorporation of fluorocarbon substituents into organic molecules is a field of continuing interest, and a variety of approaches have been reported. The research described within this thesis is concerned with the functionalisation of C-H bonds adjacent to primary or secondary hydroxyl units via free-radical additions to fluoroalkenes. A range of cyclic and acyclic alcohols and diols have been functionalised in this manner, and both substituent and electronic effects on the radical process have been investigated. Further functionalisation of the polyfluoroalkylated products has been performed, giving a range of new fluorinated systems, and an investigation into the chemistry of these systems has begun.
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Hon, Nyok-Sai. "Formation, characterization, and chemical reactions of free radicals in lignin." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54437.
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Free radicals are produced in lignin during mechanical treatment and irradiation with light of various wavelengths.
During mechanical treatment, the lignin macromolecule is degraded severely as revealed by ESR and viscosity measurements. Several types of mechano-radicals are produced in lignin during the mechanical process. Among these the phenoxy radicals are rather stable, where carbon-radicals are labile at ambient conditions. Transient mechano-radicals reacted readily with oxygen molecules to produce peroxy radicals even at 77°K, but they decayed rapidly at ambient temperature.
Photodegradation of lignin was observed when macromolecule was irradiated with light of λ<3500 Å as revealed by ESR, viscosity, and weight loss. Phenoxy radicals are the predominant intermediates in the photoirradiated lignin as shown by ESR studies. Elimination of side chains of lignin phenyl propane units took effect in α-carbonyl group bearing molecules. By contrast, β aryl ether substituents adjacent to α-carbonyl groups caused ether cleavage under identical conditions of photoirradiation. This is attributed to energy transferred from excited α-carbonyl groups to the ether bonds. The α-carbonyl groups also functioned as photosensitizers accelerating photochemical reactions of lignin.
Termination and decomposition reactions of mechano-radicals and photoinduced free radicals in lignin ultimately lead to the formation of para- and ortho-quinones, carbonyl groups, and double bonds which cause the color of lignin.
These potential choromophoric groups can be partially removed from lignin by using ultraviolet light of λ> 4000 Å; and they can be completely removed by irradiation of lignin in the presence of dioxane-water with light of λ>3500 Å. Experimental findings suggest chat chromophoric groups in lignin were being trapped or blocked by dioxanyl radicals resulting in brightening. However, the photoreduced lignin-adduct suffered color reversion. This adverse effect can be prevented by using 2-hydroxy-4-methoxy-benzophenone as a photostabilizer.
The feasibility of applying photoreduction techniques to high- yield pulps was demonstrated. However, optimal experimental conditions for photoreduction of lignin in high-yield pulps have not been established yet.Ph. D.
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Guiver, S. C. "Thermochemistry of cyclic and acyclic radicals and kinetics of their recombination reactions." Thesis, Open University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376044.
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Waygood, Steven John. "Kinetic studies of some free radical reactions involved in cloudwater chemistry." Thesis, Open University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292305.
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Lush, Rachel K. "Hydrogen atom abstraction pathways to functionalised free radicals." Thesis, University of Oxford, 2001. http://ora.ox.ac.uk/objects/uuid:84e82ee6-f8b4-4f11-a3d2-30af12f4e0b3.
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Radical translocation chemistry has classically been employed for the generation of carboncentred radicals as a means of remotely functionalising nominally unreactive sites. Previous work within the group had investigated vinyl radicals to effect translocation and had identified a need for a more reactive abstracting radical. In this regard, the high energy of alkoxyl radicals would facilitate rapid 1,5-hydrogen abstraction as opposed to simple reduction. This thesis describes the use of alkoxyl radicals, generated from N-alkoxyphthalimides, to abstract a hydrogen atom selectively from the α-position of a lactam ring. Alkoxyl radicals generated from precursors designed to lead to intramolecular trapping of the translocated radical were prone to β-scission in preference to 1,5-hydrogen atom abstraction. This is attributed to a combination of developing π-overlap in the transition state and stabilisation of the resulting radical both by nitrogen and the attached alkyl substituents. Incorporation of an alkenyl trap onto the lactam ring led to successful 1,5-hydrogen atom abstraction and stereoselective cyclisation, although β-scission remained the dominant pathway. Translocation initiated by nitrogen-centred radicals was investigated and it was found that 1,5-hydrogen abstraction occurred in preference to β-scission; intramolecular trapping of the translocated radical proved impossible either because the precursors were unstable to the reaction conditions or because increased steric bulk impeded hydrogen abstraction by the less reactive aminyl radical. Preparation of bicyclic pyrrolidinones via successive 5-endo-5-exo-trig cyclisations was investigated; the precursors were found to undergo direct reduction in preference to cyclisation. Alkyl or aryl groups attached to the a-acylamino carbon may lead to preferential 5-endo cyclisation by stabilisation of the developing radical in the transition state.
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Thompson, David Francis. "Iron (III) mediated ring expansion / cyclisation reactions." Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297007.
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Shen, Youqing. "Atom transfer radical polymerization and its continuous processes /." *McMaster only, 2001.
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Jiang, Shengdong. "SYNTHESIS OF NOVEL BENZIMIDAZOLIUM PERFLUORO MODEL COMPOUNDS USING FREE RADICAL REACTIONS AND SYNTHESIS OF NOVEL LIGANDS SUBJECT TO BOTH FREE RADICAL AND ROMP POLYMERIZATION REACTIONS FOR FABRICATING ANION-EXCHANGE MEMBRANES." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/theses/2359.
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In the first part of this thesis, three different structures of perfluoro-benzimidazolium polymers were designed. Three benzimidazole model compounds were also designed to mimic the actual membranes. The three model compounds were synthesized via multiple steps and connected with fluorine tags via free radical based reactions. The first one is 1,3-dimethyl-2-phenyl benzimidazole with two methyl protecting groups on the phenyl ring; the second one is 1,3-dimethyl-2-phenyl benzimidazole with two phenyl protecting groups on the phenyl ring; and the third one is 2-phenyl benzimidazole with no protecting group on the phenyl ring as a reference. A new model reaction was developed to bond benzimidazolium ligands with perfluorohexyl iodine. The free radical substitution used Cp2Fe and H2O2 as a radical initiator under a mild condition. The stability of those model compounds under alkaline condition (3 M NaOD/MeOD/D2O at 80 °C) can be tested using NMR methods. In the second part of the thesis, a novel AIBN-norbornene structure was synthesized and used as a free radical initiator for polymerization of pentafluoroethyl trifluoro vinyl ether to yield a perfluoro chain with a norbornene structure at the end. The norbornene structure provides a position for further polymerization with Grubbs catalyst and cyclooctene-triphenyl-phosphonium salt. Under Grubbs second generation catalyst, both rings on norbornene side and cyclooctene side were undergone ring-opening metathesis polymerization to form a long hydrocarbon chain. The positively charged triphenyl-phosphonium group serves as an anion-exchange group for better conductivity. Then, all the double bonds on polymer were reduced by hydrogenation and form a half hydrocarbon half perfluoro polymer. This type of hybrid polymer can be combined with PTFE to provide better mechanical strength and water uptake. The bulky anion exchange group also expect to provide alkaline stability.
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Skene, William G. "Investigation of nitroxide-mediated thermal and photochemical reactions of living free radical polymerization." Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6351.
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The work presented in this thesis deals primarily with living free radical polymerization (LFRP). Two main specific areas of this process have been studied; thermal and photochemical reaction sequences. Stoichiometric unimolecular initiators were found to be ideal probes for studying the reactions involved in the LFRP process. The bond dissociation energy (BDE) of the labile C-O bond of the alkoxyamine initiators was found to be ca. 28 kcal/mol and is dependent on the resulting carbon centered radical produced upon thermal decomposition. Lower activation energies were measured for more stable carbon centered radicals. Complementary to the thermal studies, photoacoustic studies (PAC) involving photochemical decomposition of the initiators led to the homolytic N-O and C-O bond cleavages in addition to disproportionation product formation. The BDE for the N-O bond of these initiators is ca. 43 kcal/mol. These studies also provided insight into volume effects, where a strict homologous solvent series is not required for extrapolating true enthalpies of reactions and volume correction factors for PAC. The decomposition quantum yields of a series of ketone based actinometers used for PAC BDE studies were re-evaluated and found to be solvent independent. The specific kinetics of thermal LFRP were equally investigated through the use of probes which are normally used for thermal initiation. Fast time resolved techniques of laser flash photolysis (LFP) were used to measure the bi-molecular rate constant for the coupling reaction between a carbon centered radical and a nitroxide radical involved in LFRP. Typical values lay in the area of 108 M-1 s-1 and are influenced by the structure of the carbon centered radical and not that of the nitroxide. The rate constants were observed to be slower with more stable carbon centered radicals, similar to the BDE results where weaker dissociation energies were observed. The formation of minor disproportionation products upon thermal decomposition of the unimolecular initiators was assigned to a concerted four center elimination ultimately responsible for the lack of controlled polymerization with acrylates. The incorporation of steric effects into the monomer or the nitroxide suppressed the formation of these products by increasing the energy barrier necessary for correct orbital alignment required for the elimination reaction. Living polymerization of acrylate monomers was achieved with a nitroxide containing bulky substituents in its 2 and 6 positions. Moderate success of living polymerization was also achieved with acrylate type monomers through the use of an additional phase not miscible with the bulk phase. Chromophores producing triplet states upon excitation were found to undergo fast and efficient energy transfer to a covalently linked alkoxyamine subsequently promoting C-O bond homolysis. The orientation of the C-O bond relative to the chromophore in addition to the distance separating the two influences the efficiency of energy transfer and bond cleavage. Using a benzophenone type chromophore with a covalently linked alkoxyamine initiator promoted photoinduced living type polymerization of acrylate.
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Denha, Abdulahad Matti. "Rate and mechanism of some free radical reactions of importance in atmospheric photochemistry." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278274.
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Diart, Valerie. "The control of selectivity in free radical reactions : a mechanistic and synthetic approach." Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283194.
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Gawler, Kate Susan. "Kinetic studies of halogen oxide free radical reactions of importance in the atmosphere." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1446416/.
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The aim of this research was to characterise the kinetics of key gas phase reactions between free radicals which occur in the atmosphere. In particular, the reactions that have been focused on are reactions where uncertainties are apparent in the reported kinetics and are: CIO + CIO + M C1202 + M CIO + H02 → HOC1 + 02 BrO + BrO → Products In the atmosphere, subsequent production of halogen atoms (X = CI, Br) following these reactions leads to ozone loss. X + 03 XO + O2 and repetition of these radical reactions renders this ozone loss process catalytic. Under sunlit conditions the self or cross-reactions of CIO or BrO constitute the rate limiting step in the ozone loss process. Consequently, accurate knowledge of the rate coefficients and products of these reactions under appropriate atmospheric conditions is essential when assessing the extent of halogen-induced atmospheric ozone depletion. These reactions were studied using flash photolysis coupled with UV absorption spectroscopy. The spectroscopy incorporated charge coupled device (CCD) technology, which facilitated rapid timescale broad band data acquisition giving rise to accurate and unequivocal monitoring of multiple species. Classical or numerical models were used to simulate experimental data by optimising kinetic parameters. The improvements in both accuracy and precision of radical monitoring associated with the CCD studies have led to a considerable improvement in our understanding of the roles of these free radical reactions in the Earth's atmosphere.
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佐藤, 章徳. "Studies on Free Radical Reactions to Form Carbon-Phosphorus and Carbon-Sulfur Bonds." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/78026.
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Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第14582号
工博第3050号
新制||工||1454(附属図書館)
26934
UT51-2009-D294
京都大学大学院工学研究科材料化学専攻
(主査)教授 大嶌 幸一郎, 教授 檜山 爲次郎, 教授 松原 誠二郎
学位規則第4条第1項該当
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Fortier, Chanel. "Preparation, Characterization, And Application of Liposomes in the Study of Lipid Oxidation Targeting Hydroxyl Radicals." ScholarWorks@UNO, 2008. http://scholarworks.uno.edu/td/889.
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In the onset of many chronic illnesses including Parkinson’s, Alzheimer’s, and cardiovascular diseases, there is evidence to support the delicate balance between prooxidant and antioxidant species is shifted in favor of the former. Under these conditions, many reactive oxygen species (ROS) including hydroxyl radicals, are generated. Hydroxyl radicals formed in close proximity to DNA, nucleotides, proteins, and lipids rapidly oxidize these biological molecules in a nonspecific way. However, their toxicity is limited by their short lifetimes. Currently, the mechanism by which hydroxyl radicals are involved in the onset of many illnesses, particularly with regard to lipid peroxidation, has yielded some controversy in the literature. Conventional studies which generate hydroxyl radicals with Fenton chemistry through bolus additions of iron and hydrogen peroxide do not mimic conditions found physiologically because there is a steady-state concentration of hydrogen peroxide concentration found in normal cellular systems. Also, former reports that used fluorescent fatty acids or free probes intercalated within liposomal membranes did not have the probes covalently attached to the phospholipids making up the liposomes. Thus, the actual placement of the probes over the analysis time may vary with experimental conditions. The objective of this research project was to prepare, characterize, and employ liposomes as models for cell membranes during free radical oxidation. Also, compared to the popularly-used technique of electron spin resonance, (ESR), our aim was to use a fluorescence-based approach which yielded the advantages of high sensitivity, fast analysis time, and less expensive equipment requirements. Degradation of fluorescently-tagged liposomes with probes covalently bound to the phospholipids was correlated with the ability of hydroxyl radicals and other possible reactive oxygen species to penetrate into the liposomes to deeper into the lipophilic layer. However, alone this experimental setup may not fully define the mechanistic role of hydroxyl radicals in lipid oxidation. Thus, a complementary approach embracing the use of MALDI-TOF mass spectrometry, lipophilic scavenger studies, and the effects of cholesterol and temperature allow a deeper understanding of the radically-driven oxidation of lipids. It was determined that hydroxyl radicals were generated and reacted with three fluorescent probes.
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Fabre, Indira. "Experimental and theoretical mechanistic studies of transition-metal free and copper-catalyzed reactions." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEE033/document.
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Cette thèse présente des travaux de méthodologie de synthèse et des études mécanistiques. Une approche complémentaire est utilisée, avec des résultats expérimentaux et des résultats théoriques issus de calculs DFT. Trois réactions ont été étudiées. La première réaction est l’alpha-arylation de cétones énolisables en l’absence de métal de transition. Elle se déroule en présence de DMF et de tBuOK. L’étude mécanistique met en évidence la formation d’une espèce riche en électrons par déprotonation du solvant. La deuxième réaction étudiée est la N-arylation de pyrazoles via la formation d’aryldiazoniums in situ. Cette réaction est catalysée au cuivre. Une évaluation de la méthode DFT la plus adaptée est présentée. Un double cycle catalytique est proposé, faisant intervenir le complexe de cuivre et l’acide acétique. La dernière réaction étudiée est la formation stéréoselective d’alkényl thioethers fluorés trisubstitués par catalyse au cuivre. La méthodologie de synthèse est présentée, suivie d’une étude mécanistique. Celle-ci révèle un mécanisme radicalaire qui peut être généralisé à d’autres substratsIn this thesis, synthetic methodology development and mechanistic studies are presented. A complementary approach, using both experiments and theoretical outcomes from DFT, is used. Three reactions were studied. The first reaction is the transition-metal free alpha-arylation of enolizable ketones. It proceeds using DMF and tBuOK. The mechanistic study reveals the formation of an electron-rich species by deprotonation of the solvent. The second reaction studied is the copper-catalyzed N-arylation of pyrazoles with arenediazonium salts generated in situ. A benchmark is performed to evaluate the best DFT methodology. A double catalytic cycle is proposed, involving copper and acetic acid. The last reaction studied is the copper-catalyzed stereoselective access to trisubstituted fluorinated alkenyl thioethers. The development of the methodology is presented. Then a mechanistic study reveals a radical mechanism that can be generalized to other substrates
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Hoffman, William Christopher. "Synthesis of fused carbocycles from benzoic acids via radical and anionic annulation procedures /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487331541711284.
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Dowey, Una. "Co-contaminant removal of mercury and hydrocarbons from soil using oxidative free radical reactions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0007/MQ28932.pdf.
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Laine, Patrick L. "Laser flash photolysis studies of halogen atom reactions of atmospheric interest." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42817.
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The Earth's atmosphere is a large photochemical reactor consisting primarily of N2 (~78%) and O2 (~21%) with Ar and water vapor being the next most abundant constituents. All of the remaining gases in the atmosphere are referred to as 'trace gases', and they play a critical role in understanding climate change, urban air quality, ozone production and depletion, and in determining the overall 'health' of the atmosphere. These trace components are present in our atmosphere with mixing ratios, i.e., mole fractions, ranging from sub parts per trillion to several hundred parts per million. One class of trace constituents that play a critical role in atmospheric chemistry are free radicals. Free radicals are highly reactive, often initiating the oxidation of natural and anthropogenic atmospheric species, thereby often controlling the fate and lifetimes of these species. The research comprising this dissertation focuses on laboratory studies of the kinetics and mechanisms of free radical (atomic halogen) reactions that can impact the levels of important trace atmospheric species. In the studies reported herein, laser flash photolysis (LFP) was coupled with time resolved atomic resonance fluorescence (RF) spectroscopic detection of Cl or Br atoms to investigate halogen atom chemistry. The research addresses three groups of reactions: Cl atom reactions with alkyl bromides, Cl and Br-initiated oxidations of small (C2-C6) alkenes, and Cl reactions with CH3SCH3 (DMS, dimethylsulfide) and CH3SeCH3 (DMSe, dimethylselenide).
The alkyl bromide reactions were experimentally unique in that we were able to deduce kinetics of the Cl atom reaction with bromoethane, n-bromopropane, and 1,2-dibromoethane by monitoring the appearance of the Br product by LFP-RF. The Br is formed via elimination that occurs essentially instantaneously following β-H abstraction by the Cl atom. All three of the bromoalkanes investigated are emitted into the atmosphere primarily from anthropogenic sources and all three have been identified by the World Meteorological Organization (WMO) as very short-lived (lifetime less than 6 months) source gases with significant ozone depletion potentials (ODPs). Additionally, the bromoalkanes mentioned above have been of interest as model compounds for larger partially halogenated organics found in the atmosphere, and they have been considered as potential replacement compounds for chlorofluorocarbons (CFCs) that have been banned as a result of the Montreal Protocol. Brominated very short-lived compounds are thought to contribute 20-25% of total stratospheric bromine. Thus, there is considerable interest in understanding the atmospheric chemistry of even the most short-lived organic bromine compounds. Temporal profiles of Br atoms provided important kinetic and mechanistic insight for the reactions over a wide range of temperature and pressure. Temperature-dependent rate coefficients are determined for the alkyl bromides of interest for the first time, and the potential importance of the Cl reaction as an atmospheric degradation pathway for each alkyl bromide is qualitatively assessed.
The studies of halogen atom reactions with alkenes focused on formation of weakly-bound adducts where kinetics of adduct formation and dissociation as well as non-adduct forming channels were evaluated. The elementary steps in the Br initiated oxidation of the alkenes 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-2-butene (tetramethylethylene, TME), and 1,3-butadiene have been investigated. The experimental kinetic database for these reactions is quite sparse. The kinetic results reported herein, suggests that Br reaction with the above olefins is much faster than previously thought. Analysis of the temperature dependence of the "approach to equilibrium" kinetic data in conjunction with electronic structure calculations allows for determination of enthalpy and entropy changes associated with each addition reaction. Where possible, both forward addition and reverse dissociation channels as well as H-abstraction pathways were characterized. The enthalpy change associated with the addition reaction to give the Br−isoprene and Br−1,3-butadiene adducts has been determined for the first time and the bond dissociation enthalpy obtained for the Br−TME adduct is in reasonable agreement with the only other previously reported value. It should be noted that in the case of isoprene and 1,3-butadiene, there are multiple possible adducts that could be formed. In order to help clarify which adducts are more or less likely to be formed, we rely on electronic structure calculations (see Chapter 5) to aid in our overall understanding of the adduct forming channels. Furthermore, for the Br reactions with the three alkenes above, atomic Br kinetics have been monitored directly both in the absence and in the presence of O2 which allowed, for the first time, determination of rate coefficients for the elementary steps in the overall complex mechanism including determination of the Br−olefin + O2 rate coefficient.
Also included in this group of reactions is the chlorine reaction with isoprene. In addition to the well-known fact that isoprene is emitted into the atmosphere from vegetation, a potentially significant marine source of isoprene has received considerable attention. Chlorine has long been thought to exist primarily in marine environments, however, recent findings also suggest a significant Cl production rate in the middle of the continental United States. There are numerous room temperature kinetic studies for the Cl + isoprene reaction in the literature, however, there is only one temperature dependent study reported. Current recommended 298 K rate coefficients for isoprene reactions suggest the Cl reaction is ~ 4x faster than the analogous OH reaction. If indeed this is the case, the Cl reaction could play a non-neglibible role in isoprene oxidation in atmospheric locales where Cl concentrations are relatively high. In addition, the C−Cl bond strength in Cl−C5H8 is obtained from direct measurements of the forward and reversible addition rate coefficients. Our results are compared with the literature data, and the potential importance of Cl-initiated oxidation as an atmospheric sink for isoprene is assessed.
The final group of reactions investigated involves reactions of Cl with DMS and DMSe. DMS and DMSe are the most prevalent sulfur and selenium compounds emitted to the atmosphere from the oceans. The oxidation of DMS has been studied extensively due to the interest in the possible role of DMS oxidation in the formation of sulfate aerosols, however, DMSe oxidation processes have hardly been studied at all. And, DMSe oxidation products are likely to be less volatile than the analogous DMS species. Selenium is an essential nutrient for many plants and animals; however, there is a fine line between enough and excess selenium which can be toxic. Most studies suggest that atmospheric deposition is an important source of Se contamination, and it is therefore critical to evaluate the source emissions and fate of Se in the atmosphere. Since the majority of atmospheric Se exists in the form of DMSe, determination of the kinetics and oxidation mechanisms of DMSe will go a long way towards understanding the global biogeochemical cycle of Se.
Both reversible addition and H-abstraction pathways have been characterized, and the first experimental determination of bond strength of the gas-phase DMS−Cl and DMSe−Cl adducts have been obtained.
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Donahue, Matthew G. "Studies toward the synthesis of the C₁₉ quassinoid polyandrane." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1127227359.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xxiii, 454 p.; also includes graphics (some col.). Includes bibliographical references (p. 246-259). Available online via OhioLINK's ETD Center
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Tamada, Mayumi. "Kinetics of free-radical reactions with monoterpenes in the aqueous phase mimicing atmospheric aerosol chemistry." California State University, Long Beach, 2013.
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Saunders, S. M. "Kinetics of some gas phase free radical reactions studied by discharge flow/resonance fluorescence methods." Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355558.
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Furze, John D. "A study of the substitution, carbonylation and free radical reactions of some transition metal complexes." Thesis, Kingston University, 1989. http://eprints.kingston.ac.uk/20525/.
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Sanyal, Debraj. "Isoindoline nitroxide antioxidants : a spin trapping investigation of the radical reactions of biologically important substrates." Thesis, Queensland University of Technology, 1999.
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Crites, Charles-Oneil. "Investigating the Interactions between Free Radicals and Supported Noble Metal Nanoparticles in Oxidation Reactions." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/33404.
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This thesis studies the interaction between free radical species and supported noble metal nanoparticles (silver and gold) in the context of oxidation reactions. The peroxidation of cumene is the first reaction to be discussed and the difference in peroxidation product distribution using silver nanoparticles (AgNP) versus gold nanoparticles (AuNP) is examined. Specifically, cumyl alcohol is obtained as the major product obtained when using supported AuNP, whereas cumene hydroperoxide is favoured for AgNP. Such variations in product distribution are partially explained by the differences in the nanoparticle Fenton activity, where the TiO2 support was proposed to enhance such activity due to possible electron shuttling capabilities with the nanoparticle surface. Use of hydrotalcite as a support was found to minimize this characteristic, due to its insulator properties. The stability of hydroperoxide was tested in the presence of various others supports (activated carbon, Al2O3, ZnO, SiO2 and clays) with little success, with hydroperoxide exhibiting stability in the presence of HT. Using an oxygen uptake apparatus, the interaction of the cumyl peroxyl radical with the AuNP surface was demonstrated. Furthermore, this interaction promotes decomposition leading to the corresponding alkoxyl radical and subsequent hydrogen abstraction to form the observed cumyl alcohol product. The radical interaction with supported nanoparticles, and its reversibility appear different for gold and silver and accounts for a large part of the product distribution differences observed between AuNP and AgNP, as illustrated below.
The peroxidation of ethylbenzene and propylbenzene was studied and revealed the participation of a reactive surface oxygen species due to the decomposition of peroxyl radicals on the nanoparticle surface. The reactive oxygen species was found to be transient in nature in the case of AuNP . Furthermore, this surface species was found to be an important participant in hydrogen abstraction leading to peroxide product formation. Finally, supported nanoparticle catalyzed tetralin peroxidation was investigated to determine the influence of temperature on the peroxidation product distribution and how changes in the reaction temperature can effect the radical-nanoparticle surface interactions.
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Pan, Xiong. "Theoretical Studies of Atmospheric Water Complexes." PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/1163.
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Intermolecular complexes between H₂O and atmospheric species HO, HO₂, H₂O₂, O₃, NO and NO₂ have been studied by ab initio molecular orbital methods. The studies have been performed to the MP2 theory level by using 4-31G, 6-31G, D95, 6-31G**, D95**, 6-311G**, 6-311+G**, 6-311++G**, 6-311+G(2d,lp) and 6-311+G(2d,2p) basis sets. The geometries were fully optimized. The vibrational frequencies were calculated. The Basis Set Superposition Error (BSSE) were estimated. Finally, the binding energies of the complexes were predicted with other thermochemical properties. The binding energies of H₂O•HO, H₂O•HO₂, H₂O•H₂O₂, H₂O•O₃, H₂O•NO and H₂O•NO₂ are estimated to be 5.7±0.6, 8.9±1.0, 7.3±1.3, 1.8±0.2, 1.17 (no BSSE correction) and 2.98 (no BSSE correction) Kcal/Mol, respectively. The Kcq for dimerization to yield H₂O•HO, H₂O•HF, H₂O•HO₂, H₂O•H₂O and H₂O•H₂O₂ are estimated to be 0.11, 2.8, 3.3, 0.067 and 0.11 atm¯¹, respectively. The H₂O•HO, H₂O•HF, H₂O•HO₂, H₂O•H₂O and H₂O•H₂O₂ are quite strongly bonded complexes, while H₂O•O₃, H₂O•NO and H₂O•NO₂ are only weakly bonded complexes. The Kcq changes with temperature are discussed, and their importance in atmospheric chemistry are addressed.