Dissertations / Theses on the topic 'Free radicals (Chemistry)'
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1
Qureshi, Tariq. "Spin chemistry." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365292.
2
Mills, Tim. "Studies in free radical chemistry." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342465.
3
Imrie, Christopher. "The chemistry of free radicals containing a ferrocenyl moiety." Thesis, University of Strathclyde, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390393.
4
梁韻詩 and Wan-sze Leung. "High resolution spectroscopy of free radicals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31237319.
5
Leung, Wan-sze. "High resolution spectroscopy of free radicals /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19737610.
6
Crockett, Rowena. "Generation of free radicals from heterocyclic compounds." Thesis, University of Aberdeen, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290239.
Abstract:
Tetrazolinones, thiatriazole 1-oxides and meso-ionic oxatriazoles were investigated as sources of free radicals. Mono-substituted tetrazolinones decomposed at their melting points. Nitrosation and nitration of the tetrazolinone ring was unsuccessful, although alkoxyalkylation of the ring took place in ether in the presence of nitrosomium and nitronium tetrafluoroborate. The tetrazolinone ring was photolytically unstable, and both eliminated nitrogen and cycloreverted. γ-irradiation of the naphthyl deivative caused cleavage of the nitrogen-hydrogen bond to give a radical which was identified by spin trapping and esr spectroscopy. Thiatriazolyl radicals were generated from thiatriazol-1-ium salts by reduction over sodium metal. Deuterium and nitrogen-15 labelled diphenylthiatriazolium salts were prepared in the reaction between thiatriazole 1-oxides and phosphorus pentachloride or pentabromide. This allowed an unambiguous assignment of the nitrogen and hydrogen hyperfine coupling constants in the esr spectrum of the unlabelled thiatriazolyl radical. X-ray crystallographic analysis was carried out on single crystals of 2,4-diphenyl-2,5-dihydro-1,2,3,5-thiatriazol 1-oxide and 2,4-diphenyl-2H-1,2,3,5-thiatriazol-1-ium bromide. Meso-ionic oxatriazolones were relatively stable to thermolysis, whereas oxatriazolimines decomposed at their melting points. The oxatriazolones decomposed on photolysis via two mechanistic pathways, while the oxatriazol-imines were resistant to photolysis. Radicals were generated by γ-irradiation and oxidation via decomposition of the heterocyclic ring. Electrochemical reduction of nitrophenyl derivatives allowed an investigation of radicals in which the heterocyclic ring was remote from the radical centre. Photochemical reaction between the nitrophenyl derivatives of the oxatriazole and tetrahydrofuran produced oxy-nitroxide radicals which were realatively long-lived and in which the heterocyclic ring was intact. The rates of hydrolysis and crystal structures of three diacetylazolinones, including diacetyltetrazolinone were investigated with the aim of determining whether a correlation existed between bond lengths and reactivity. The relative rates of hydrolysis were found to be independent of the bond lengths. However a correlation was found between the rates of hydrolysis and the acidity of the unsubstituted azolinones.
7
Robles, Eric San Jose. "Electronic spectroscopy of jet-cooled organometallic free radicals /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487776801323524.
8
Towle, Jonathan Peter. "The LMR spectra of free radicals." Thesis, University of Oxford, 1992. http://ora.ox.ac.uk/objects/uuid:7ac8e9e4-33e8-428b-962d-943bf07d5f94.
Abstract:
Laser Magnetic Resonance (LMR) is a very sensitive, accurate and high resolution spectroscopic technique. Transitions of paramagnetic species are brought into coincidence with a fixed frequency laser using Zeeman tuning. Three different LMR spectrometers are described, two of which use the CO laser as a radiation source and the other used optically pumped far-infrared lasers. These LMR spectrometers have been used to study four radicals, germanium hydride (GeH), tellurium deuteride (TeD), iron hydride (FeH) and iron deuteride (FeD). Transitions in the fundamental and first hot bands of the GeH radical have been detected by CO LMR. The transitions occur within both 2Π1andfrasl;2 and 2Π3andfrasl;2 manifolds. These data have been fitted with previously published data for GeH and GeD to determine the parameters of a single model effective Hamiltonian which describes all naturally occurring isotopomers. Details of the Hamiltonian are given. The same Hamiltonian was used to model transitions in the fundamental and first two hot bands of the TeD radical that were also recorded using CO LMR. Resonances from the seven most abundant isotopomers, including the two with I = ½, have been identified. Seven transitions in the fundamental band of FeH have been observed using Faraday CO LMR. Due to the complicated electronic structure for FeH it is not possible to model these data using a single model effective Hamiltonian. It has been possible to fit the parameters of a second order Zeeman expression to these FeH data and so determine accurate zerofield transition wavenumbers for six of these transitions. Pure rotational transitions in the ground state of FeD have been observed using FIR LMR. As for FeH the parameters of second order Zeeman expressions can be fitted to these transitions and zero field wavenumbers determined.
9
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.
Abstract:
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.
10
Wood, Geoffrey Paul Farra. "Theoretical Investigations of Radical-Mediated Protein Oxidation." Thesis, The University of Sydney, 2006. http://hdl.handle.net/2123/1413.
Abstract:
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
Wood, Geoffrey Paul Farra. "Theoretical Investigations of Radical-Mediated Protein Oxidation." University of Sydney, 2006. http://hdl.handle.net/2123/1413.
Abstract:
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.
12
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.
Abstract:
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.
13
Zaidi, Naveed Ahmed. "Ring opening/cyclisation in oxiranyl carbinyl free radicals." Thesis, Loughborough University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303179.
14
Black, Michael. "Gas phase cyclisation reactions of aromatic free radicals." Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/10822.
15
Pushkarsky, Michael B. "High resolution spectroscopy and photochemistry of the free radicals /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488202678773409.
16
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.
Abstract:
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.
17
Wright, N. G. "Laser induced fluorescence studies of some simple free radicals." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354707.
18
Huang, Horng-Chih. "Total syntheses of (+,-) pleurotin and (+,-) dihydropleurotin acid /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487584612165839.
19
Fitzpatrick, James Alexandr John. "Hyperfine structure in the excited electronic states of free radicals." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288579.
20
Burrows, Jeremy N. "Free radical methodology and approaches to the synthesis of roseophilin." Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:a2bd60aa-c369-4412-aea1-d93a6eab07db.
Abstract:
The homolytic Brook rearrangement is discussed and homolytic fragmentations of epoxides and epoxysilane chemistry are reviewed. Thiyl radical induced isomerisation was performed on spiro alkenylepoxysilanes to generate novel alkenyl-α-trimethylsilylaldehydes rather than the products of radical Brook rearrangement. The trimethylsilylaldehydes were shown to isomerise on heating to silyldienol ethers and, via the addition of a Grignard reagent, to act as stereoselective vinyl cation equivalents. Attempts to extend the scope of the isomerisation to non-rigid systems met with failure. A review of the antibiotic Roseophilin is presented. Cycloaddition-fragmentation approaches to medium and large rings are reviewed as a prelude to our first route, the proposed Michael addition-retro-aldol fragmentation of the Diels-Alder adduct derived from isopropyl-cyclopentadiene and cyclodec- 2-yn-1-one. The novel ynone, synthesised via the intramolecular Friedel-Crafts acylation of 10-trimethylsilyl-9-decynoyl chloride, was found to isomerise readily to bicyclo[4.4.0]dec-1(6)-en-2-one therefore the model Diels-Alder reaction with cyclopentadiene was effected in one-pot from the cyclisation precursor. Details of the attempted fragmentation of tricyclo[10.2.1.02,11]pentadeca-2(11),13-dien-3-one are then described but, due to inconclusive results, an alternative study was instigated. The use of free-radical macrocyclisations in the synthesis of large rings is reviewed with particular reference to the synthesis of natural products. Three strategies for the formation of a bicyclo[10.2.1]pentadecanone skeleton are reported, and subsequent model studies described. Cuprate additions to vinyl lactones and epoxides are discussed. The preferred strategy, involving a cycloalkyl tether between the radical donor and radical acceptor groups, was extended to a system which was derived from the addition of various cuprates to 2-oxabicyclo[3.3.0]oct-7-en-3-one The preparation of cuprates derived directly from 6-iodohexan-1-ol and 1-chloro-6-iodohexane is described. The trans- cuprate addition products were converted successfully to bicyclo[10.2.1]pentadec-12-en-3-one, and the cis- analogues, accessible through a novel regio- and stereoselective hydroboration-fragmentation reaction of 7- (6'-chlorohexyl)-2-oxabicyclo[3.3.0]oct-7-en-3-one, led to bicyclo[10.2.1]pentadec- 13-en-3-one. The successful cyclisations of model oximes, to form nitrones having the correct connectivity for the third ring of Roseophilin, are described. Cuprate additions to 6-(1'-methylethyl)-2-oxabicyclo[3.3.0]oct-7-en-3-one resulted in anti- attack; the cis- adducts were inaccessible via the above methodology but a few intermediates in the trans- series were prepared. Future routes and modifications to the methods developed are then discussed.
21
Ma, Tongmei, and 馬彤梅. "Cavity ringdown laser absorption spectroscopy of free radicals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B30137342.
22
Kirsop, Peter James. "Determination of the philicity of the aryl radical." Thesis, University of Aberdeen, 2007. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=217986.
Abstract:
Radicals, like other functional groups, may be classed as nucleophiles or electrophiles depending upon their character. Much has been done in the past to determine the· nucleophilicity or electrophilicity of a wide ra~ge of radicals, but it .. does not appear that the philicity ofthe aryl radical has yet been determined. A competitive cyclisation of an aryl radical to one of two alkyl chains containing olefins ofdiffering electron density was undertaken to determine aryl radical philicity. Prior to cyclisation, synthesis of the precursors was required, starting from simple commercially available aromatic compounds. A wide range of allyloxy aromatic compounds with different substituents on the two olefins was synthesised. In the course of the required multi-step synthesis many previously unreported compounds were isolated and fully characterised, including crystal X-ray diffraction studies where crystals were obtained. To investigate the effects of different electron density in the aryl ring a further range of competitive cyclisation precursors were synthesised with an ester group para to the site where the aryl radical is formed. Studies into the synthesis of a competitive cyclisation precursor with olefin bearing side chains with no heteroatom were also undertaken. The procedure for the cyclisation reactions and subsequent work-up was optimised under both conventional and microwave methodology. Analysis of the products was performed using both quantitative and qualitative analytical techniques. Quantitative analysis was performed using gas chromatography, IH NMR spectroscopy with an internal standard and isolation of products. Qualitative analysis was performed using both ID and 2D NMR spectroscopy. Analysis of the results of the competitive cyclisation reactions show beyond reasonable doubt that the aryl radical is nucleophilic in character.
23
Crosby, David. "Preliminary studies of the reactions of alkenyl α-nitroalkyl free radicals." Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/26974.
Abstract:
The mechanistic fate of alkenyl α-nitroalkyl free radicals generated in the following reactions has been studied: SRN1 reactions between α-bromonitro compounds and nucleophiles, reductive reactions between α-substituted nitro compounds and tri-n-butyltin(IV)hydride (Bu3SnH) or 1,4-dihydro-N-benzylnicotinamide (BNAH), oxidative reactions between alkenyl nitronate anions and nucleophiles and the photolytic rearrangement of α-iodonitro compounds have all been studied.
24
Ritchie, A. J. D. "Chemically induced dynamic electron polarisation of transient free radicals in solution." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354864.
25
Rhodes, C. J. "Structural studies of organic and organosilicon free radicals by ESR spectroscopy." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370439.
26
Gillett, David Alan. "Transient free radicals studied by laser magnetic resonance spectroscopy." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:038bdb7e-1f8c-4112-bcea-4a0ca7ab7bcf.
Abstract:
A liquid nitrogen cooled, carbon monoxide laser magnetic resonance spectrometer was used to study mid-infrared vibration-rotation transitions in the gaseous free radical NCO, in its ̅X2Π state, at very high resolution. The use of an intracavity absorption cell made possible the observation of some transitions with sub-Doppler resolution. Developments to the spectrometer extended the range of operation of the CO laser. Most importantly, a CO laser operating on overtone transitions, Δν = 2, was operated in Oxford. The Δν = 2 CO laser operates over the range 2450-3800cm-1 (4.08-2.63 μm), and the Δν = 1 CO laser over the range 1200-2100 cm-1 (8.33-4.76 μm). NCO exhibits a Renner-Teller effect in its ground electronic state, an interaction between the motion of the electrons and the bending motion of the nuclei. Vibration-rotation transitions were observed in a sequence of bands involving the excitation of the out-of-phase stretching vibration, in the region of 1900cm-1. Some of the bands involved the excited bending vibration. The Zeeman effect behaviour of the molecular energy levels, particularly in the 2Σ vibronic states, clearly showed the manifestation of the Renner-Teller effect. The Zeeman effect in the 2Σ vibronic states was considered in detail. Many of the 2Σ LMR spectra were recorded at sub-Doppler resolution. NCO is complicated to model, and unassigned LMR spectra remain. A harmonic Renner-Teller model was developed for the analysis. It was implemented by constructing an explicit matrix representation of the single electronic state N2 effective Hamiltonian, which was diagonalised exactly. A new term in this Hamiltonian, describing centrifugal distortion corrections to the Renner-Teller coupling term, was developed for the 2Σ vibronic states in order to account for anharmonic vibronic interactions.
27
Modglin, James D. "A computational study of the chemistry of 3-phenylpropyl radicals." Virtual Press, 2005. http://liblink.bsu.edu/uhtbin/catkey/1328118.
Abstract:
Using computational methods, we have investigated the chemistry of 3-phenylpropyl radical systems. These systems are of importance to polymer chemistry as free radical additions involving these species are integral in the production of styrene-containing plastics. Although the addition reactions have been well studied, the other reaction pathways, namely f3-fragmentation and cyclization, have not been as comprehensively studied. As a result, our computational study involved 3-phenylpropyl radical systems that had been systematically mono-substituted at five positions, two on the propyl chain and three on the aromatic ring. This computational analysis consisted of calculation of optimized geometries and energies for reactants, products, and transition states, followed by examination of derived thermochemical quantities (enthalpies of activation and reaction), and critical structural parameters (transition bond lengths and bond angles) of the systems. Finally correlation of structure and reactivity of the various systems was attempted. Density functional theory (DFT) using the B3-LYP functional and the 6-31 G(d) basis set was selected as the level of theory.Department of Chemistry
28
Wright, Rossana Rubino. "High resolution, rotationally resolved, electronic spectroscopy of free radicals : MgCH3, MgNC and HCCs /." The Ohio State University, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487949508372479.
29
Lampiao, Fanuel. "Measurement of free radicals and their effects on human spermatozoa." Thesis, Link to the online version, 2006. http://hdl.handle.net/10019/212.
30
Smith, Kamilah. "Semi-quantitative detection of free radicals using spin trapping and phosphorus-31 NMR spectroscopy." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79130.
Abstract:
In this study the effectiveness of quantitative 31P nuclear magnetic resonance (NMR) spectroscopy in conjunction with spin trapping to detect and quantify various free radical species was investigated. Initially the research was focussed on assigning the 31P NMR signals for hydroxyl and superoxide radicals and on identifying the quantitative reliability of the technique. The radical adduct reaction products (diamagnetic species), of hydroxyl (HO·) and superoxide (O2 -·) radicals with phosphorus containing nitroxides, were determined to be relatively stable and as a result the 31P NMR chemical shifts for these species were determined. Their structures were verified and quantified using 31P NMR in the presence of a phosphorus containing internal standard. The 31P NMR chemical shifts for 5-diisopropylphosphoryl-5-methyl-1-pyrroline-N-oxide (DIPPMPO) and 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) spin traps with a variety of carbon centered radicals were also determined.A novel equilibrium reaction involving molecular oxygen and alkaline hydrogen peroxide was investigated and it was found that the concentration of superoxide radicals present in a system of alkaline hydrogen peroxide is affected by the nature of gas with which it is in equilibrium. The concentration of superoxide radicals was determined to be significantly larger than that of hydroxyl radicals at elevated pH values.
Experiments have shown that NMR in conjunction with spin trapping can be a valuable tool for the detection and quantification of radical species.
31
Simpson, Nigel J. K. "Studies of transient free radicals in solution by flash photolysis E.S.R." Thesis, University of Oxford, 1990. http://ora.ox.ac.uk/objects/uuid:dd9a8aa9-f68a-4362-af7e-6c052fa3a5fe.
Abstract:
An introduction is presented to the nature of polarized and non-polarized transient spin resonance signals, produced by flash-photolysis e.s.r., followed by a description of the equipment used for experimental work. Theories of Chemically Induced Dynamic Electron Spin Polarization are reviewed and various models introduced to illustrate these concepts. A description is given of the first thorough investigation into the effect of CIDEP polarization transfer down a free radical chain and expands upon the consequences of hyperfine-dependent relaxation and the relative signs of coupling constants in various radical species. It concludes with an account of two methods of kinetic analysis which are the first practical demonstrations of their kind, and employ extension of expressions developed in earlier chapters. Studies are made of the CIDEP behaviour of radicals in high viscosity paraffins. A reassessment of previous published work is made: anomalous polarization behaviour was found to have been over-compensated for. A new method of extracting values for T1 and T2,/sub> is demonstrated for strong transient e.s.r. signals. A collection of experimental data relating to the previously unexplained absorptive polarization observed in the spectrum of ketyl radicals and the longer-time phase inversion of hyperfine-dependent CIDEP is given. The operation of Triplet Mechanism CIDEP in the ketyl radical systems is ruled out and a division of radicals into geminately formed and free-encounter pairs is shown to be incapable of explaining the observed phase changes. In its place a cross-relaxational mechanism, drawing upon simultaneously generated nuclear spin polarization is advanced. Conclusions are drawn that this may account for both anomalies. Lastly a photochemical application of CIDEP is demonstrated; two different reaction intermediates are identified upon photolysis of ortho phthalaldehyde, depending upon the quenching conditions. A reaction scheme consistent with all experimental data is proposed. A brief comment upon the photo-chemistry of indan 2-one concludes this work.
32
Gopalakrishnan, Sandhya. "Electronic spectroscopy of the alkoxy radicals." Columbus, OH : Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1051024461.
Abstract:
Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xxiv, 173 p.: ill. (some co.). Includes abstract and vita. Advisor: Terry A. Miller, Dept. of Chemistry. Includes bibliographical references (p. 171-173).
33
Oredsson, Sven. "Reperfusion injury in skeletal muscle with special reference to oxygen-derived free radicals as mediators /." Lund : Dept. of Surgery, Helsingborg Hospital, 1994. http://catalog.hathitrust.org/api/volumes/oclc/39056318.html.
34
Flint, Nicholas John. "A study of linewidth variation in the E.S.R. spectra of some radical anions." Thesis, Lancaster University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329999.
35
Bakioğlu, Levent. "Polymerization and characterization of poly(ethyl methacrylate)." Ankara : METU, 2003. http://etd.lib.metu.edu.tr/upload/1081363/index.pdf.
36
Donato, Karen Ann. "Graft polymerization of methyl methacrylate onto polytetrafluoroethylene free radicals." Ohio : Ohio University, 1985. http://www.ohiolink.edu/etd/view.cgi?ohiou1183996024.
37
Bopegedera, A. M. Ranjika Priyadarshi. "Dye laser and diode laser spectroscopy of gas phase free radicals." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184695.
Abstract:
The gaseous free radicals, alkaline-earth metal monoalkylamides, monoacetylides, monoformamidates and monopyrrolidates, consisting of a metal atom (Ca or Sr) bonded to a single ligand, were synthesized in a Broida oven. The electronic and vibrational structures of these molecules were studied by low-resolution laser spectroscopy techniques. These inorganic molecules are ionic, well represented by the structure M⁺L⁻ (M = Ca, Sr: L = ligand). Three electronic transitions were identified for the metal monoalkylamides and the metal monoformamidates. The formamidate anion bonds to the metal in a bidentate fashion through the oxygen and nitrogen atoms. Two electronic transitions were observed for the metal monopyrrolidates. The pyrrolide anion ring bonds to the metal to provide these "open-faced sandwich" type molecules with pseudo-C₅ᵥ symmetry. For the metal monoacetylide molecules, only one electronic transition (Ā²Π-Ẋ²Σ⁺) was observed. Several vibrational frequencies were determined for these inorganic molecules from the low-resolution spectra. The Ā²Π-Ẋ²Σ⁺ transition of the calcium monoacetylide molecule was rotationally analyzed at high-resolution using the filtered laser excitation spectoscopy technique. The rotational line positions were fitted to a ²Π-²Σ⁺ Hamiltonian to obtain several rotational constants. The calcium-carbon bond length in CaCCH was calculated for the ground (2.248 Å) and excited (2.200 Å) electronic states. The vibration-rotation spectra of the gaseous bismuth hydride and bismuth deuteride molecules were recorded, using a diode laser system. The 1-0 fundamental band and several hot bands with Δv-1 were rotationally analyzed. The rotational line positions were fitted first, to a Dunham energy expression and then to a ³Σ⁻ Hamiltonian, to obtain ground state rotational constants. The bismuth-hydrogen (deuterium) bond distance was calculated to be 1.809 Å (1.807 Å).
38
Frum, Coriolan Ioan. "High-resolution Fourier transform infrared spectroscopy of high-temperature molecules and free radicals." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185468.
Abstract:
High resolution absorption spectra of the IF molecule in the X¹Σ⁺ ground state were observed with the Kitt Peak Fourier transform spectrometer in a F₂/I₂ flame. Iodine fluoride is the most unstable interhalogen compound. Accurate wavenumber measurements (±0.0002 cm⁻¹) were made for the 1-0, 2-1 and 2-0 bands and molecular constants were derived. The observation of a high resolution emission spectrum at 13 μm (750 cm⁻¹) is unusual. Seven bands (1-0 through 7-6) of the main isotopic form, ²⁸Si³²S, were observed along with three bands (1-0, 2-1 and 3-2) for each of the minor species, ²⁹Si³²S, ³⁰Si³²S and ²⁸Si³⁴S. More than 2450 lines were fitted for this important astrophysical molecule. Dunham coefficients were obtained for each isotopomer of SiS. Mass-reduced Dunham parameters, including Watson's correction due to the breakdown of the Born-Oppenheimer approximation, were also derived from the data. The first high resolution spectrum of a metal dihalides was recorded by infrared emission spectroscopy. The infrared emission spectrum of BeF₂ was observed in the region of the antisymmetric stretching mode, ν₃, and the combination band, ν₁ + ν₂. Eight vibration-rotation bands were rotationally analyzed and the spectroscopic constants are reported. The equilibrium beryllium fluoride bond distance (rₑ) was found to be 1.3729710(95)Å in BeF₂. Values of the vibrational frequencies of all the three normal modes were obtained from the spectra. The gas phase infrared spectrum of C₆₀ (buckminsterfullerine) has been observed in emission with the National Solar Observatory Fourier transform spectrometer at Kitt Peak. Bands attributable to the C₆₀ molecule are found at 527.1 cm⁻¹, 570.3 cm⁻¹, 1169.1 cm⁻¹ and 1406.9 cm⁻¹. Additional emission features are tentatively assigned to C₇₀ or combination bands of C₆₀. A new, strong emission is observed at 1010.2 cm⁻¹ belonging to an unknown molecule. A new electronic state of ³Π symmetry of PtO has been observed between 7100 cm⁻¹ and 8015 cm⁻¹ above the ground state. This new state was observed through an electronic transition to the ³Σ⁻ ground state of this free radical. Three independent electronic systems connecting the Ω = 0,1 and 2 spin components in the upper state to Ω = 1 component in the ground state have been recorded in emission with the Fourier transform spectrometer associated with the McMath Solar Telescope at Kitt Peak. (Abstract shortened with permission of author.)
39
Patterson, Hazelyn. "The design and construction of an apparatus for low-temperature dimerization of aliphatic free radicals." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 1997. http://digitalcommons.auctr.edu/dissertations/2805.
Abstract:
This study documents an effort to design and construct an apparatus for the continuous generation hydrogen atoms to convert aliphatic and aromatic molecules to their respective dimers, by free radical mechanisms. The addition of hydrogen atoms to alkene and aromatic molecules, and hydrogen atom abstraction from alkanes by atomic hydrogen, followed by dimerization or disproportionation has been extensively studied. Emphasis here is placed on proving the efficacy of this device by production of known dimeric products.
This prototype incorporates critical factors known to effect gas phase free radical dimerizations and attempts to address each. Close attention then, has been paid to the temperature of the reacting gases and the tendency of the intermediates to disproportionate. This device introduces pre-cooled substrate molecules, at atmospheric pressure, to a perpendicular stream of hydrogen atoms produced by electrical discharge. The argon purged reaction chamber is packed with glass wool to enhance three body collisions and promote dimerization. The conversion of isobutene, benzene and toluene to dimers in this device was studied. Products were separated via simple distillation and product determinations made by comparing GC-Mass Spec peaks with the literature.
40
Huang, Meng. "Spectroscopy Studies of Free Radicals and Ions Containing Large Amplitude Motions." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515012236254284.
41
Manandhar, Sudha. "Free Radical Induced Oxidation, Reduction and Metallization of NiSi and Ni(Pt)Si Surfaces." Thesis, University of North Texas, 2010. https://digital.library.unt.edu/ark:/67531/metadc31542/.
Abstract:
NiSi and Ni(Pt)Si, and of the effects of dissociated ammonia on oxide reduction was carried out under controlled ultrahigh vacuum (UHV) conditions. X-ray photoelectron spectroscopy (XPS) has been used to characterize the evolution of surface composition. Vicinal surfaces on NiSi and Ni(Pt)Si were formed in UHV by a combination of Ar+ sputtering and thermal annealing. Oxidation of these surfaces in the presence of either O+O2 or pure O2 at room temperature results in the initial formation of a SiO2 layer ~ 7 Å thick. Subsequent exposure to O2 yields no further oxidation. Continued exposure to O+O2, however, results in rapid silicon consumption and, at higher exposures, the kinetically-driven oxidation of the transition metal(s), with oxides >35Ǻ thick formed on all samples, without passivation. The addition of Pt retards but does not eliminate oxide growth or Ni oxidation. At higher exposures, in Ni(Pt)Si surface the kinetically-limited oxidation of Pt results in Pt silicate formation. Substrate dopant type has almost no effect on oxidation rate. Reduction of the silicon oxide/metal silicate is carried out by reacting with dissociated NH3 at room temperature. The reduction from dissociated ammonia (NHx+H) on silicon oxide/ metal silicate layer shows selective reduction of the metal oxide/silicate layer, but does not react with SiO2 at ambient temperature.
42
Hulvey, Glenn A. "Internal pressure's role in the selectivity of the bromine radical." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06102009-063106/.
43
Malkin, Tamsin Leanne. "Detection of free-radicals and other species ti investigate atmospheric chemistry in the HIRAC chamber." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515362.
44
Wohaieb, Saleh A. "Oxygen free radical scavenging systems in clinical and experimental (chemical and spontaneous) diabetes mellitus." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27567.
Abstract:
The extent to which endogenous free radical-scavenging defense mechanisms
are involved in experimental and human diabetes was investigated in various tissues of animals with chemically-induced or spontaneous diabetes (BB Wistar rats) and in erythrocytes of patients with either Type I or Type II diabetes. Diabetes was induced in female Wistar rats using alloxan (ALX) or streptozotocin (STZ), each administered in a dose of 50 mg/kg body wt., intravenously. The present study also included a group -of animals in which body wt. loss was induced by food-deprivation for 72 h. The effects of pharmacological interventions (insulin or allopurinol (ALP)), on these processes were also investigated in chemically-induced diabetes., The activities
of catalase (CAT), CuZn-superoxide dismutase (CuZn-SOD), glutathione peroxidase (GSH-PX) and glutathione reductase (GSSG-RD) as well as levels of reduced glutathione (GSH) were examined in heart, pancreas, liver and kidney as well as in erythrocytes. Erythrocytes were also examined for their susceptibility
to in vitro oxidative stress induced by hydrogen peroxide (H₂0₂). Criteria studied in this regard were GSH-depletion and malondi-aldehyde (MDA) production (an index of lipid peroxidation).
The results obtained showed that tissue antioxidant systems are altered in experimental diabetes and that the magnitude of the alterations increased with the degree of body weight loss. Furthermore, the duration of hypoinsulinemia might contribute to the nature of alterations in antioxidant mechanisms. The complex patterns of the alterations observed varied from one tissue to another and may be the result of compensatory increases, usually involving enzymes whose activity in the particular tissue may be limiting, and direct inhibitory effects of endogenous oxidants on the enzymatic
components of tissue antioxidant systems.
The ability of insulin (9-12 U/kg body wt., subcutaneously) to reverse the many similar alterations of tissue antioxidant enzymes in diabetes induced by either STZ or ALX suggests that these changes are more likely attributable to hypoinsulinemia rather than to direct effects of either diabetogenic drug. The above-mentioned effects indicate that insulin can markedly influence tissue antioxidant status. However, the reason for the persistence of decreased CuZn-SOD activity in both liver and kidney of ALX-diabetic rats after 12 wk of treatment with insulin is not clear at present, and requires further investigation to determine whether this reflects the presence of a residual deficit in tissue antioxidant processes in liver and kidney despite insulin treatment, or whether it is the result of a direct effect exerted by ALX. Acute ALP administration (50 mg/kg body wt., intraperitoneally) was associated with reductions in ketonuria and early mortality among ALX-diabetic rats, and long-term ALP treatment (1.9 mg/day in drinking water) resulted in a normalization of renal CuZn-SOD activity in these animals.
Comparable (although not identical) changes in tissue antioxidant status are present in insulin-dependent spontaneously diabetic BB (ISDBB) rats and in animals made diabetic by STZ or ALX administration. Our data also demonstate that the alterations in tissue GSH levels characterizing ALX-diabetes more closely paralleled changes seen in the ISDBB rat than did those in the diabetic state induced by STZ. If the alterations in antioxidant
status in uncontrolled chemically-induced diabetes are attributable to a lack of insulin, the observed changes in ISDBB rats are suggestive of sub-optimal insulin therapy in these animals.
The results obtained from BB rats demonstrate two types of alterations in antioxidant status: strain-related differences (increased CAT activity in pancreas and decreased GSH levels in pancreas and liver of both ISDBB and their non-diabetic littermates (NDLM)) and diabetes-related changes (mani- fested by an increase in cardiac GSH content and increases in activities of cardiac CAT and GSSG-RD, pancreatic CuZn-SOD and GSSG-RD, and renal GSH-PX). Whether or not these "strain-related" alterations in antioxidant status increase the susceptibility of these animals to developing diabetes remains unknown.
Certain alterations were observed in red cells from diabetic patients and from animals with experimental diabetes suggesting that these alterations
are more likely to be diabetes-related than species-dependent. Red cells in chemically-induced and clinical diabetes showed an increased resistance
to peroxide-induced depletion of GSH, an effect attributed to hyperglycemia,
which results in an increased supply of NADPH through the hexose monophosphate shunt for regeneration of GSH from GSSG via the GSSG-RD system. However, the susceptibility of red cells from diabetic patients and animals to lipid peroxidative damage was increased as reflected in augmented MDA production. In addition, insulin treatment did not normalize MDA production in red cells subjected to oxidative challenge and vigorous insulin treatment in both ALX- and STZ-diabetic rats resulted in a markedly decreased MDA production in response to H₂0₂. Moreover, GSSG-RD activity
of red cells was increased in both uncontrolled and insulin-treated diabetic animals as well as in diabetic patients.
However, some differences in erythrocyte antioxidant enzymes were also observed in erythrocytes from diabetic subjects and animals. For example, diabetic patients showed an increased activity of CuZn-SOD, while erythrocytes
from diabetic animals showed no alterations in the activity of this enzyme. Erythrocyte membrane NADH-dehydrogenase activity was increased only in diabetic patients with Type I diabetes, but not in Type II diabetes or in diabetic animals. Erythrocytes from ALX- and STZ-diabetic animals showed an increase in the activity of GSH-PX and those from NDLM BB rats showed a decrease in CAT activity, alterations that were not observed in human diabetes.
Finally, as far as antioxidant defense mechanisms are concerned, our results suggest that diabetes is associated with some common alterations in these mechanisms regardless of the model (chemically-induced versus the spontaneous type of diabetes) or the species used (animal versus human diabetes). Some of these alterations seem to be influenced by the degree of diabetic control, while others are apparently independent of it. Future studies will focus on the extent to which alterations in red cells of human diabetics can be used to predict the development of long-term sequelae of the disease.Medicine, Faculty of
Anesthesiology, Pharmacology and Therapeutics, Department of
Graduate
45
Wilks, Justin. "Free Radical Chemistries at the Surface of Electronic Materials." Thesis, University of North Texas, 2010. https://digital.library.unt.edu/ark:/67531/metadc31552/.
Abstract:
The focus of the following research was to (1) understand the chemistry involved in nitriding an organosilicate glass substrate prior to tantalum deposition, as well as the effect nitrogen incorporation plays on subsequent tantalum deposition and (2) the reduction of a native oxide, the removal of surface contaminants, and the etching of a HgCdTe surface utilizing atomic hydrogen. These studies were investigated utilizing XPS, TEM and AFM. XPS data show that bombardment of an OSG substrate with NH3 and Ar ions results in the removal of carbon species and the incorporation of nitrogen into the surface. Tantalum deposition onto a nitrided OSG surface results in the initial formation of tantalum nitride with continued deposition resulting in the formation of tantalum. This process is a direct method for forming a thin TaN/Ta bilayer for use in micro- and nanoelectronic devices. Exposure to atomic hydrogen is shown to increase the surface roughness of both air exposed and etched samples. XPS results indicate that atomic hydrogen reduces tellurium oxide observed on air exposed samples via first-order kinetics. The removal of surface contaminants is an important step prior to continued device fabrication for optimum device performance. It is shown here that atomic hydrogen effectively removes adsorbed chlorine from the HgCdTe surface.
46
Furneaux, Kate Louise. "Field studies of the chemistry of free-radicals in the troposphere using laser induced fluoresence spectroscopy." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507714.
47
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.
Abstract:
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.
48
Merle, John Kenneth. "Computational studies of gas-phase radical reactions with volatile organic compounds of relevance to combustion and atmospheric chemistry." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1126305456.
Abstract:
Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xvii, 259 p.; also includes graphics (some col.). Includes bibliographical references (p. 233-259). Available online via OhioLINK's ETD Center
49
Moffat, Karen Ann. "Synthesis and evaluation of model initiator/reversible terminating adducts for the stable free radical polymerization process." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0002/NQ42755.pdf.
50
Dunn, Kerri, and kerri dunn@deakin edu au. "Chiral organotin hydrides as enantioselective reducing agents." Deakin University. School of Nutrition and Public Health, 2000. http://tux.lib.deakin.edu.au./adt-VDU/public/adt-VDU20061207.142326.
Abstract:
This thesis reports on the feasibility of the utilization of organotin hydrides as enaantioselective free radical reducing agents. The chiral organotin hydrides prepared contain the bulky chiral (1R,2S,5R)-menthyl substituent and in some cases also contain a stereogenic tin centre. Reaction of (1R,2S,5R)-menthylmagnesium chloride (MenMgC1) with triphenyltin chloride in THF proceeds with epimerization of the C-1 carbon of the menthyl group and results in a mixture of (1R,2S,5R)-menthyltriphenyltin and (1S,2S.5R)-menthyltriphenyltin. Addition of Lewis bases such as triphenylphosphine to the THF solution of triphenyltin chloride prior to the addition of the Grignard reagent suppresses epimerization and enables isolation of pure (1R,2S,5R)-menthyltriphenyltin. (1R,2S,5R)-Menthyltriphenyltin is the precursor for the synthesis of (1R,2S,5R)-menthyldiphenyltin hydride as well as (1R,2S,5R)-menthyl-containing organotin halide derivatives. A crystal structure of (1R,2S,5R)-menthylphenyltin dibromide and (1R,2S,5R)-menthylphenyltin dichloride confirmed the configuration of the menthyl substituent in these compounds.
Reaction of MenMgC1 with diphenyltin dichloride in THF proceeds with no epimerization of the C-1 carbon of the menthyl group and bis((1R,2S,5R)-menthyl)diphenyltin is formed. A crystal structure of (1R,2S,5R)-menthyltriphenyltin confirmed the configuration of the menthyl substituent. Bis((1R,2S,5R)-menthyl)diphenyltin is used to form bis((1R,2S,5R)-menthyl)phenyltin hydride as well as other bis(1R,2S,5R)-menthyl derivatives.
A series of chiral non-racemic triorganotin halides and triorganotin hydrides containing one or two (1R,2S,5R)-menthyl substituents as well as various potentially intramolecular coordination substituents were synthesized and characterized. The intramolecular substituents include the 8-(dimethylamino)naphthyl, 2-[(1S)-1-dimethylaminoethyl]phenyl, 2-(4,4-dimethyl-2-oxazoline)-5-methylphenyl and the 2-(4-(S)isopropyl-2-oxazoline)-5-methylphenyl substituents.
Each compound containing a stereogenic tin centre was synthesized as diastereomeric mixtures. AM1 calculations of these compounds provide good qualitative predictability of the molecular geometries observed in the solid state as well as the diastereomeric ratios observed in solution. X-ray analysis of some of the organotin halides containing intramolecular coordination substituents revealed a tendency towards penta-coordination at the tin centre as a result of N-Sn interactions.
The chiral organotin hydrides synthesized were found to be poor enantioselective free radical reducing agents. However, the addition of one molar equivalent of achiral or chiral Lewis acids to the free radical reduction reactions involving these organotin hydrides results in remarkable increases in enantioselectivity. There are numerous examples in which enantioselectivities exceed 80% and three examples of enantioselectivites which are equal and above 90% with one outstanding enantioselective outcome of ≥99%. These results appear to be the highest enantioselectivites for organotin hydride radical reductions reported to date.
There is strong evidence to suggest that the chiral menthyl group of the organotin hydride directs the stereochemical outcome in the reduced product. The results also suggest that an increase in the number of menthyl substituents attached to tin or the introduction of intramolecular coordination substituents does not necessarily results in a greater increase in enantioselectivity.
Preliminary studies into the synthesis of organotin hydrides containing Lewis acid functionalities are also reported. A zirconium chloride functionality was found to be incompatible with organotin hydride. However, an organotin hydride containing a trialkylboron Lewis acid functionality attached via an alkyl chain was successfully synthesized. Although this reagent was only stable in the preparative THF solution, it was still found to be effective at reducing benzaldehyde to benzyl alcohol.