To see the other types of publications on this topic, follow the link: Intermediates (Chemistry).
Dissertations / Theses on the topic 'Intermediates (Chemistry)'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Intermediates (Chemistry).'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Yang, Hongfang. "Benzotriazole intermediates in organic chemistry." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0005743.
Full text
2
Hughes, K. J. "Chemistry of gaseous organosilicon reactive intermediates." Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/33745.
Full textAbstract:
Chapter one provides a brief history and current state of knowledge of the chemistry of organosilicon reactive intermediates relevant to this thesis. Chapter two outlines the experimental techniques used in the majority of work carried out in this thesis. Chapter three describes an experimental investigation of the pyrolysis of 4-dimethylsilylbut-l-ene and 5-dimethylsilylpent-l-ene, with and without excess methylchloride as a silyl radical trap. The results of computer modelling of the pyrolysis of 4-dimethylsilylbut-1-ene with excess methylchloride are described, in which information concerning the isomerisation of an alpha-silyl radical to a silyl radical via a hydrogen shift is obtained. Chapter four describes the results of an experimental investigation of the reactions of dimethylsilene and dimethylsilylene with anions. Chapters five and six contain the results of computer modelling of three related pyrolysis mechanisms composed of complex series of unimolecular rearrangements of silylenes, silenes, disilenes and disilacyclopropanes. Chapter seven describes an experimental determination of Arrhenius parameters for the trapping of dimethylsilene by butadiene, together with the results of pyrolysis of butadiene adducts of methylsilene, dimethylsilene and dimethylsilylene. Chapter eight is an experimental investigation of the pyrolysis of cis and trans dimethy1(1-propenyl)vinylsilane with excess 2,3-dimethylbutadiene as a silylene trap. Interpretation of the results as a cis-trans isomerisation and decomposition of the cis isomer via a silacyclopropane intermediate are reinforced by the results of computer modelling of both systems. Chapter nine describes an experimental investigation of the pyrolysis of 1, 2-dimethyldisilane with and without butadiene as a silylene trap. Computer modelling of the pyrolysis with the absence of butadiene is used to clarify the pyrolysis mechanism. Chapter ten is an experimental investigation of the pyrolysis of silacyclobutane and methylsilacyclobutane with excess butadiene to trap silylene intermediates and thus suppress secondary decomposition. Arrhenius parameters for the primary decomposition pathways are determined.
3
Fonkeng, Beshakeh. "Reductive Chemistry of Dicyanoalkane Reactive Intermediates." TopSCHOLAR®, 1990. https://digitalcommons.wku.edu/theses/2353.
Full textAbstract:
Radical ions are reactive intermediates that are both radicals and ions (either a radical cation or a radical anion). The intrinsic properties of radical ions are not yet well -characterized. Such knowledge is mechanistically important to the organic chemist.
The specific question that motivates this research is as follows: is it possible to controllably express free radical processes in a radical ion independent of ionic chemistry (and vice versa) and, if so, what factors dictate which type of chemistry is expressed?
Our investigation focused on the chemistry of radical anions of dicyanoalkanes that are formed upon metal reduction. Factors influencing this chemistry such as solvent effects were also studied. This study represents a small segment of a larger study of five functional group classes of molecules, that will ultimately involve a description of the chemistry of radical anions. The goal of the overall project is to attain a generalized view of the chemistry of radical anions of bifunctional organic molecules.
The results obtained suggest that free-radical processes (cyclization and polymerization) can be expressed within radical anions. Furthermore, our results show that free -radical polymerization as opposed to cyclization is the dominant mode of reaction. Such an observation has not been established before for radical anion systems.
The requisite background information regarding what is known about these reactive intermediates to date, and rationalization as to why more information is needed through this, and the work of other scientists, is laid out in the following introduction.
4
Gregory, M. F. "Organometallic intermediates." Thesis, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356021.
Full text
5
Gordon, Charles M. "Organometallic intermediates." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334789.
Full text
6
Mustafa, Hussein Habeeb. "Studies to provide new intermediates for industrial chemistry." Thesis, Bangor University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664482.
Full textAbstract:
This project examines a number of aspects of the development of products for application in industry. This project consists of three parts. The first part investigated optimising an industrial process leading to (S)-4-benzyloxazolidin- 2-one (1). This study has secured a protocol which allows its preparation in high yield and at lower cost. The second part is concerned with the development of a cheap method to access pheromones containing diene, triene and tetraene groups, using acetal (58) derived from the ozonolysis of cyc1onona-l ,4,7 -triene. The third part of the study entails the use of the same Z,Z,Z-cylonona-l,4,7-triene to synthesize novel bis and tris-cyc1ic allenes with eleven and twelve membered rings.
7
Henry, Cyril. "The trapping of reactive intermediates using flow chemistry." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/369350/.
Full textAbstract:
Flow chemistry, long established in the bulk chemical industry has recently received more attention in fine chemicals production and discovery chemistry with small-scale apparatus, resulting from laboratory equipment becoming commercially available. The interest in flow chemistry is driven in part by the precise control of reaction parameters, the automation and sequencing of reactions and facile access to certain areas of reaction space. The approach of flow chemistry is rather different to conventional batch chemistry. The dispersion of fluids and the thermic transfer were discussed. By taking advantage of working in a flow chemistry domain, the generation and trapping of ketenes from thermolysis of alkynyl ethers was developed. Kinetics and activation energy were determined by means of in-situ IR spectroscopy using conventional and improved methodologies. Generation of ketene such as methylene ketene, acyl ketene and vinyl ketene from dioxinone and Meldrum’s acid was also investigated under flow chemistry conditions. Coupled to a custom design of a photo-reactor, the flow apparatus was adapted to perform relevant synthesis of photochemical reaction such as [2+2] cycloaddition, arylation of alkene and SRN1 type reaction. Enabling better access to photochemistry, this photo-flow platform overcomes many limitations associated with batch reactors.
8
Thomas, Gareth Leslie. "Chemistry of electrophilic intermediates in the sulfonation process." Thesis, Swansea University, 2002. https://cronfa.swan.ac.uk/Record/cronfa43090.
Full textAbstract:
The study is more specifically concerned with the reactions of aromatic sulfonic anhydrides. The study was carried out in order to gain more knowledge on the reactions and behaviour of aromatic sulfonic anhydrides, and the role they play in the formation of sulfones in the industrial sulfonation process. An introduction to industrial sulfonation as used in the detergent industry is included. It has been proposed that sulfones are formed in the sulfonation process, by reaction of sulfonic anhydrides with alkylbenzene (starting material). An initial study of the reactions of p-toluenesulfonic anhydride with toluene using different catalysts was carried out, providing background knowledge for the more detailed studies that followed. A number of competition reactions were completed, investigating the influence of substituents in a series of arenes on the relative rates of reaction of p-toluenesulfonic anhydride. Studies were carried out using nitromethane as solvent and AlCl3 as catalyst. Included in the study is a review of the synthesis of diaryl sulfones, and the synthesis of a number of unsymmetrical sulfones. A new route to di-tolyl sulfone was identified from intramolecular reaction of p-toluenesulfonic anhydride catalysed by AlCl3. The relative rate of formation of sulfones via this route compared to Friedel-Crafts type sulfonylation reactions and was studied. The relative rates were found to be very low. The synthesis of a series of aromatic sulfonic anhydrides was carried out using direct sulfonation with SO3. The sulfonic anhydrides were then used to investigate the effect of substituents on the rates of reaction of substituted benzenesulfonic anhydrides reacting with toluene. The reactions were carried out in nitromethane using AlCl3 as the catalyst.
9
Kirk, Martin. "Reactions of gaseous borane intermediates." Thesis, University of Leeds, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305836.
Full text
10
Carpenter, A. J. "Heteroaromatic synthesis using metallated intermediates." Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380046.
Full text
11
Haynes, Anthony. "Intermediates in organometallic photochemistry." Thesis, University of Nottingham, 1989. http://eprints.nottingham.ac.uk/27829/.
Full textAbstract:
CHAPTER 1: A background to the techniques of matrix isolation, liquid xenon solution and flash photolysis with fast IR detection is presented. The application of infrared spectroscopy in structural studies of metal carbonyl compounds is also discussed. Chapter 2: Photolysis of((nu5-C5R5)Pt(CO))2 (R=H, Me) in frozen gas matrices results in production of ((nu5-C5R5)Pt2(mu-CO)). 13CO enrichment and polarised photochemistry show that the photoproduct contains a single symmetrically bridging CO group. Photolysis of (CpNi(mu-CO))2 in frozen gas matrices results in formation of CP2Ni2(CO) with a terminal CO ligand. The stability these dinuclear photoproducts in room temperature solution has been investigated using fast TRIR spectroscopy. Photolysis in CO matrices leads to M-M bond cleavage and reaction with CO to give Pt(CO)4 or Ni(CO)4 as the final product. CHAPTER 3: Photolysis of Os2(CO)9 or OS2(CO)8- - (mu-nu1, nu1-C2H4) in frozen gas matrices leads to formation of Os2(CO)8, which has only terminal CO groups. The thermal and photochemical reactivity of Os2(CO)a towards CO, N2 and C2H4 is investigated. Photolysis using plane polarised light provides confirmation of the C2v structure of Os2(CO)9, and gives evidence favouring a D2h structure for Os2(CO)8. Prolonged UV photolysis of Os2(CO)9 in CO matrices leads to cleavage of the Os-Os bond and production of Os(CO)5. CHAPTER 4: The mechanism of the photochemical deoligomerisation of FpSiMe2SiMe3 is investigated using a variety of techniques. The reaction is shown to proceed via two photochemical steps. Primary CO-loss is followed by intramolecular trapping to give a silyl(silylene) intermediate. The second step involves expulsion of an SiMe2 fragment and coordination of a ligand. L. to give CpFe(CO)(L)SiMe3 (L = CO, PPh3,C2H4 or N2). CHAPTER 5: A study of the photochemistry of Fp-disilyl complexes containing beta-silyl hydrogens implies beta-H transfer from Si to Fe as the dominant process following photodissociation of CO. The product, a metalladisilacyclopropane or nu2-disilene complex, is implicated as an intermediate in the photochemical formation of FpH in this system. CHAPTER 6: The experimental techniques and spectrometers used in this research are described. along with a discussion of the theory and advantages of FTIR spectroscopy.
12
Sullivan, Ann Marie G. "Resonance Raman spectra of chloroperoxidase reaction intermediates." VCU Scholars Compass, 1992. https://scholarscompass.vcu.edu/etd/5610.
Full textAbstract:
Chloroperoxidase is an enzyme that exhibits spectroscopic and structural properties similar to cytochrome P-450. Chloroperoxidase is studied using resonance Raman spectroscopy to characterize the reaction intermediates of the physiological mechanism, known as compounds I and II. Compound I is formed by a two electron oxidation of the resting enzyme and contains an Fe(IV) porphyrin ℼ cation radical. A one electron reduction of compound I produces the compound II intermediate which contains an oxy-ferryl [Fe(IV)=O] iron heme.
Chloroperoxidase is a heme enzyme of substantial interest because of its structural similarity to cytochrome P-450 and because of its diverse reactivity. Chloroperoxidase can function as a peroxidase, catalase, haloperoxidase and to some extent as a monooxygenase. Chloroperoxidase is excreted by the mold, Caldariomyces fumago and contains the iron protoporphyrin IX prosthetic group. From previous spectroscopic data, it has been determined that native chloroperoxidase is a penta-coordinate heme with a cysteine thiolate axial ligand.
The reaction intermediates of chloroperoxidase, compounds I and II, are among the least stable of the known peroxidase intermediates. However, they can be stabilized somewhat by avoiding the use of hydrogen peroxide as the oxidant. Because of catalase activity of this enzyme, hydrogen peroxide can act as both oxidant and substrate causing the rapid turnover of the enzyme. For the generation of the chloroperoxidase intermediates, the enzyme is mixed with an equal volume of oxidant in a Ballou four jet mixer fed by two 100 ml syringes which produces a continuous jet of newly formed intermediate. Compound I was formed by mixing the enzyme with a 15 fold excess of peracetic acid and compound II was formed by premixing the enzyme with a 100 fold excess of a substrate, ascorbic acid, then mixing with a 30 fold excess of peracetic acid.
The observed resonance Raman frequencies of the chloroperoxidase intermediates are similar to those observed for horseradish peroxidase, however there are a number of reproducible differences in frequencies due to differences in ground state symmetry or axial ligation. The in-plane skeletal modes in the resonance Raman spectrum of compound II can be assigned as follows: v10 at 1645 cm^-¹, v₃₇ at 1606 cm^-¹, v₂ at 1582 cm^-¹, v₃₈ or v¹₁₁ at 1554 cm^-¹, v₃ at 1511 cm^-¹, v₂₈ at 1476 cm^-¹, vinyl =CH₂ wags at 1345 and 1434 cm^-¹, v₂₀ or v₂₉ at 1396 cm^-¹, and v₄ at 1374 cm^-¹. These assignments are close to those previously reported for horseradish peroxidase compound II. Band assignments for compound I are v₁₀ at 1647 cm^-¹, v37 at 1619 cm^-¹, v₂ at 1589 cm^-¹ and v₄ at 1358 cm^-¹. The band at 1647 cm^-¹ is depolarized, whereas, the bands at 1619 and 1589 cm^-¹ are polarized. The oxy ferryl [Fe(IV)=O] frequency has been observed at approximately 790 cm-¹ in horseradish peroxidase. In chloroperoxidase, two bands at 790 and 753 cm^-¹ are present in both compounds I and II resonance Raman spectra. Upon ¹⁸O-substitution these bands shift approximately 30 cm^-¹ as predicted by simple force constant calculations.
13
Buckingham, Grant Thornton. "Pyrolysis and spectroscopy of cyclic aromatic combustion intermediates." Thesis, University of Colorado at Boulder, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10108707.
Full textAbstract:
We have studied the pyrolysis of aromatic combustion intermediates using an array of detection techniques. The molecules investigated include cyclic aromatic molecules with hydrocarbon substituents (ethylbenzene, n-propylbenzene, isopropylbenzene, and styrene), oxygen-containing substituents (anisole and phenol), resonance stabilized radicals (benzyl radical and tropyl radical) and phenyl radical. At the exit of a resistively heated micro-reactor (1 mm inner diameter, 3 cm long), the pyrolysis fragments are detected using photoionization mass spectrometry (PIMS), matrix isolation vibrational spectroscopy, microwave spectroscopy, tunable VUV synchrotron-based PIMS, and tabletop VUV PIMS with photoelectron photoion coincidence spectroscopy (PEPICO). This array of detection methods allows for the identification of all possible fragments including metastables, radicals, and atoms. The findings allow for detailed mechanistic information regarding which pathways are active at different pyrolysis temperatures and can also be used to help identify products and individual isomers that are formed during the gas-phase thermal decomposition of aromatic systems. By providing direct experimental pyrolysis data, models for fuel decomposition and soot formation can be improved to help understand current combustion systems and eventually aid in the design of superior fuel sources in the near future.
14
Waddell, Stewart MacKenzie. "Synthesis of intermediates related to anthracyclinones." Thesis, Heriot-Watt University, 1989. http://hdl.handle.net/10399/953.
Full text
15
Upmacis, R. K. "Catalytic intermediates in liquefied noble gases." Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373342.
Full text
16
Foley, Michael Andrew. "1-Acyldihydropyridones as Synthetic Intermediates." DigitalCommons@USU, 1988. https://digitalcommons.usu.edu/etd/7180.
Full textAbstract:
The most efficient and stereoselective total synthesis of (+/-) lausbine II to date has been achieved. The key steps in this are the copper-mediated conjugate addition reaction of the Grignard reagent of 1-bromo-4-chlorobutane to a dihydropyridone and a stereoselective reduction of a quinolizidinone.
Methodology has been developed for the convenient synthesis of 1-acyl-2-substituted-1,2,5,6-tetrahydropyridines. This was accomplished by adding novel alkylzinc iodides to the 1-acyliminium ion derived from Nphenoxycarbonyl-4-methoxy-1, 2, 3, 4-tetrahydropyridine.
17
York, David C. "Synthesis of azaacridines using nitrene intermediates." Thesis, Keele University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254883.
Full text
18
Goodman, Jennifer. "Computational studies on metallophosphoranes as intermediates in palladium-phosphine chemistry." Thesis, Heriot-Watt University, 2009. http://hdl.handle.net/10399/2267.
Full textAbstract:
The work detailed in this thesis describes density functional (DF) calculations that were performed to investigate the possible role of metallophosphoranes in the reactions of palladium-phosphine complexes. A study was conducted on X/R exchange in [M(Cl)X(PH3)(PR3)] (X = F, OH, NH2, Me, Ph, Cl; R = H, Me, F; M = Ni, Pd, Pt), to see how metallophosphorane formation, followed by R-transfer, was affected by varying the X ligand, nature of the accepting phosphine (PR3) or the metal centre. Metallophosphorane formation was easiest with the small, electronegative X ligands such as F and OH and was promoted by electron-withdrawing R substituents on the accepting phosphine. When the metal centre was varied, the trend for the activation barriers was Ni < Pd < Pt. Subsequent R-transfer was always more facile than metallophosphorane formation. The mechanism of disproportionation of [Pd(Cl)OH(PPh3)2] was studied using DF calculations on the model system [Pd(Cl)OH(PH3)2] and hybrid DF:HF methods on the full experimental complex. In the small model a reaction profile was found via a metallophosphorane intermediate formed via a transition state at 28.3 kcal/mol (from the trans reactant) or a transition state at 21.8 kcal/mol (from the cis reactant). A similar mechanism was found with the full experimental complex (highpoint 27.5 kcal/mol) but a more accessible route was located via a zwitterion intermediate, [PdPPh3Cl]-[P(OH)Ph3]+ (highpoint 26.7 kcal/mol). Possible mechanisms for experimentally-observed Ph/Ph exchange in trans- [PdX(Ph)(PPh3)2] (X = Cl, Br, I) and R/Ph exchange in trans-[PdI(R)(PPh3)2] (R = Me, CH2CF3) were studied using DF:HF calculations. For Ph/Ph exchange, the most accessible pathway involved pre-dissociation of a phosphine, followed by intermolecular attack of the palladium-bound phenyl on the remaining phosphorus. The lowest activation barriers were seen when X = I. The equivalent mechanism was also the most accessible for Me/Ph exchange, although the analogous mechanism without pre-dissociation of phosphine was very competitive. R/Ph exchange was computed to be considerably less accessible when R = CH2CF3 than when R = Me.
19
Herek, Jennifer Lynn Zewail Ahmed H. Zewail Ahmed H. "Femtochemistry and reactive intermediates : application to atmospheric and organic chemistry /." Diss., Pasadena, Calif. : California Institute of Technology, 1996. http://resolver.caltech.edu/CaltechETD:etd-04082008-084916.
Full text
20
Ye, Tao. "Catalysed asymmetric synthesis using #alpha#-diazocarbonyl intermediates." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333847.
Full text
21
Cummins, Jonathan James. "The synthesis of thiophenes from acyclic intermediates." Thesis, Nottingham Trent University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332913.
Full text
22
Alshammari, Mohammed. "Use of organometallic intermediates in organic synthesis." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/45471/.
Full textAbstract:
Chapter One: Chapter one describes a historical overview and the practical consideration of lithiation reactions and highlight of some of the factors that could influence the site of lithiation. It also provides reviews of the directed and side-chain lithiation of substituted aromatics. Chapter Two: Chapter two deals with lithiation of N′-phenethyl-N,N-dimethylurea with three equivalents of t-BuLi in THF at –78 °C followed by reaction with various electrophiles to give side-chain substituted products due to lithiation and substitution at the CH2 next to the phenyl ring (α-lithiation). The 2-lithio isomer can be obtained via Br–Li exchange of 2-bromo derivative using MeLi followed by t-BuLi in THF at –78 °C. The lithium reagents thus obtained react with various electrophiles to give the corresponding 2-substituted derivatives in excellent yields. Lithiation of N′-(3-phenylpropyl)-N,N-dimethylurea takes place on the α-CH2 with t-BuLi at 0 °C. On the other hand, lithiation of N′-(4-phenylbutyl)-N,N-dimethylurea with t-BuLi at 0 °C takes place on one of the methyl groups of the urea unit. Chapter Three: Chapter three includes lithiation of N'-(2-(2-methylphenyl)ethyl)-N,N-dimethylurea with three equivalents of n-BuLi in THF at 0 °C followed by reaction with various electrophiles to give side-chain products in excellent yields due to α-lithiation. Similarly, lithiation of the pivalamide derivative followed by reaction with benzophenone as a representative electrophile gave the corresponding α-substituted product in high yield. Surprisingly, no products resulting from lateral lithiation were observed under the conditions tried, which sharply contrast with the reported results for lateral lithiation of the carbamate derivative. Chapter Four: In this chapter, N-(2-(4-methoxyphenyl)ethyl)amine derivatives are reported to undergo directed ortho-lithiation next to the directing group with n-BuLi at 0 ºC, followed by treatment with various electrophiles, to give high yields of the corresponding substituted products. This contrasts sharply with the earlier results for the α-substitution of the pivaloyl derivative using t-BuLi at a lower temperature. Chapter Five: Chapter five includes variations in the site of lithiation of N-acyl-3-(aminomethyl)pyridine derivatives with different N-substituents using different lithiating reagents. Ring lithiation has been achieved by the use of t-BuLi at -78 °C followed by reaction with various electrophiles to give the corresponding 4-substituted products in high yields. On the other hand, the reaction was regioselective towards the side-chain when LDA was used as the lithium reagent at -20 to 0 °C. A mixture of ring and side-chain substitution products was obtained when n-BuLi was the lithium reagent. Chapter Six: Chapter six investigates the use of various chiral ligands containing different coordinating groups in Matteson homologation. Some stereoselectivity (de = 2-52%) was obtained depending on the type of chiral catalyst used. The best %de (52%) was obtained when Yb(OTf)3 as a Lewis acid and (1R,2R)-1,2-bis((R)-2,2-dimethyl-1,3-dioxolan-4-yl)ethane-1,2-diol as a chiral ligand were used in combination. However, significant %de (46%) could be obtained with the diol chiral ligand in the absence of the Lewis acid, which is very interesting and open windows for further improvement.
23
Biamonte, Marco A. "A synthetic approach to erythromycin biosynthetic intermediates." Thesis, University of Cambridge, 1995. https://www.repository.cam.ac.uk/handle/1810/272992.
Full text
24
Piro, Nicholas A. (Nicholas Anthony). "Niobium-mediated generation of P-P multiply bonded intermediates." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49552.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Vita.
Includes bibliographical references.
The diphosphaazide complex (MesNPP)Nb(N[CH2 tBu]Ar)3, 1 (Mes = 2,4,6-tri-tert-butylphenyl, Ar = 3,5-dimethylphenyl), releases a P2 unit upon heating to form MesNNb(N[CH2 tBu]Ar)3, 2, in a first-order process. The chemistry of the putative P2 intermediate was probed with a variety of reagents. It was successfully transferred to organic dienes to yield polycyclic diphosphines, and also to terminal phosphide complexes of the general formula P????M(N[R]Ar)3 to yield cyclo-P3 complexes. Coordination of W(CO)5 to 1 accelerates conversion to 2, with loss of the (P2)W(CO)5 fragment, such that this reaction occurs readily at 20 C. The (P2)W(CO)5 fragment was transferred to the same substrates listed above, as well as to a low-valent platinum source. In all cases, this transfer occurs in higher yields than for the uncomplexed P2. Kinetic measurements on the elimination reactions showed them to be first-order in diphosphaazide complex and independent of substrate concentration, consistent with the hypothesis that P2 and (P2)W(CO)5 are released into solution as discrete species. The above reaction chemistry was used to synthesize reactive, anionic cyclo-P3 complexes of niobium with formulas [f(OC)5Wgn(P3)Nb(N[CH2 tBu] Ar)3]- (n = 0;1; 2). These complexes were shown to react with the electrophiles Ph3SnCl, MesNPCl, and RC(O)Cl to yield coordinated h2-triphosphirene complexes. The acyltriphosphirene complexes [(OC)5W]2RC(O)P3Nb(N[CH2-tBu]Ar)3 are unstable toward loss of an RCP3[W(CO)5]2 fragment and formation of oxoniobium ONb(N[CH2 tBu]Ar)3.
(cont.) The cycloaddition chemistry of the so-generated, putative triphosphacyclobutadiene intermediate was probed through trapping reactions, including with adamantylphosphaalkyne to provide tetraphosphabenzenes complexed to W(CO)5. Silylphosphinidene complexes of niobium, R3SiPNb (N[CH2 tBu]Ar)3, were used to transfer phosphinidenes to isocyanates, carbon dioxide, and a terminal phosphorus monoxide complex of molybdenum in O-for-PR metathesis reactions. The latter reaction served as a synthesis of the unique, 3e?? donor diphosphenido ligand in the complex iPr3SiPPMo(N[tBu]Ar)3. Also investigated were the syntheses and reaction chemistry of metallacyclic phosphorylphosphinidene complexes, R2P(O)PNb(N[CH2 tBu]Ar)3. The niobaziridine hydride complex HNb(h2-C6H10?? NCy)(NCy2)2 was synthesized as a potential model for N2 binding, while independently prepared ([mu]-N2)[Nb(N[CH2tBu]Ar)3 was reductively cleaved to the anionic terminal nitride complex [NNb(N[CH2-tBu]Ar)3]-. Activation chemistry of As4 by Mo(N[tBu]Ar)3 and HNb(h2-tBuC(H)??NAr)(N[CH2 tBu]Ar)2 was used to ynthesize two terminal arsenide complexes. The syntheses of potential AsP- and PN-eliminating complexes are also described.
by Nicholas A. Piro.
Ph.D.
25
Velian, Alexandra. "Taming reactive phosphorus intermediates with organic and inorganic carriers." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97986.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2015.Cataloged from PDF version of thesis. Vita. Page 216 blank.
Includes bibliographical references.
Complexes (THF)₀-₂E[P₃Nb(ODipp)₃]₂ (E = Sn, Pb; Dipp = 2,6-iPr₂C₆H₃) were prepared and characterized as potential precursors to new tetrel phosphides. Treatment of (THF)Sn[P₃Nb(ODipp)₃]₂ with pyridine-N-oxide effected the formation of ONb(ODipp)₂(py)₂ and a new tin phosphide, [(THF)SnP₆]x, characterized using a multitude of techniques. Additionally, P₃Nb(ODipp)₂(py)₂, prepared from [Na(THF)₃][[P₃Nb(ODipp)₃] in the presence of pyridine and salts of coordinating cations, was found to successfully produce AsP₃ upon treatment with AsCl₃ Dimer [P₂Nb(ODipp)₃]₂ has been obtained via a novel "2(3-1)" synthetic strategy. The mononuclear diphosphorus complex P₂Nb(ODipp)₃ proposed to be generated transiently by formal P- abstraction from previously reported [Na(THF)₃][P₃Nb(ODipp)₃] undergoes irreversible dimerization to form the [P₂Nb(ODipp)₃]₂ complex, and is alternatively trapped reversibly by a 1,3-cyclohexadiene (CHD) to form in situ C₆H₈P₂Nb(ODipp)₃ Unprotected dibenzo-7[lambda]³A3-phosphanorbornadiene derivatives RPA (A= C₁₄H₁₀ or anthracene; R = tBu, dbabh, HMDS, iPr₂N, cis-Me₂ Pip, Cy₂N, Me₂N) were synthesized by treatment of the corresponding phosphorus dichloride RPCl₂ with MgA-3THF. Thermolysis of RPA benzene-d₆ solutions leads to anthracene extrusion. Experimental and computational thermodynamic activation parameters suggest this process occurs through the intermediacy of a singlet phosphinidene for the iPr₂N derivative. The [RP] unit could be transferred to CHD, a carbene and an ortho-benzoquinone, with formation of the corresponding anti-7-phosphanorbornene, phosphaalkene and phospholane. The anthracene diphosphorus adduct P₂A₂ was synthesized from Me₂NPA, through isolated intermediates CIPA and [P₂A₂Cl][AlCl₄]. P₂A₂ was found to transfer P₂ efficiently to N-₃ CHD, 1,3-butadiene and (C₂H₄)Pt(PPh₃)₂ to form 1,2-cyclo-[P₂N₃]-, P₂(CHD)₂, P₂(BD)₂ and (P₂)[Pt(PPh₃)₂]₂ . A complete kinetic and computational study of the P₂(CHD)₂ formation from P₂A₂ suggests P₂ is a productive intermediate in solution. Additionally, a molecular beam mass spectrometry study on the thermolysis of solid P₂A₂ reveals the direct detection of molecular fragments of only P₂ and anthracene thus establishing a link between solution-phase P₂-transfer chemistry and production of gas-phase P₂ by mild thermal activation of a molecular precursor. The HCP precursor Ph₃PC(H)PA was synthesized directly from C1PA. The activation of P₄ with [Na][SnPh₃ ] and sodium naphthalenide led to the synthesis of phosphide compounds [Na(benzo-15-crown-5)][P(SnPh₃)₂], P(SnPh₃)₃, (XL)₂InP(SnPh₃)₂, (Ph₃P)AuP(SnPh₃)₂, P₇(SnPh₃)₃ and P7(SiMe₃)₃, characterized using a variety of techniques.
by Alexandra Velian.
Ph. D.
26
Young, Mary Jennifer T. "The photochemistry of pentafluorophenyl azide and its transient intermediates /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487596307356436.
Full text
27
Daniels, David S. B. "Reactions of allenylpalladium intermediates in organic synthesis." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:61054889-d0ac-4d08-96a7-2e05fb3aa455.
Full textAbstract:
This thesis describes our examination of the reactivity of allenylpalladium intermediates generated from the reaction of palladium(0) with propargylic electrophiles. Chapter 1 provides a general overview of the literature reported to date concerning the nature and reactivity of allenylpalladium intermediates. The coupling of a variety of propargylic electrophiles with aryl boronic acids to form allenes is examined in Chapter 2. However, when employing diastereomerically pure electrophiles, some erosion of stereochemistry was observed in the allene products. This effect was examined further, and epimerisation of the allene product was found to be the origin of the loss of stereochemistry. Evidence for the species likely responsible for this epimerisation is presented. The serendipitous formation of tetrahydrofurans (THFs) from propargylic 7-membered cyclic carbonates prompted an in-depth examination of this reactivity, as described in Chapter 3. The reaction of these cyclic carbonates was rendered stereoselective and the stereochemical outcome of the reaction elucidated. The methodology was extended to propargylic acyclic carbonates which allowed the formation of tetrahydropyrans (THPs). The effect of ring-size and substituents on the cyclisations was examined, culminating in the formation of two rings in a single step from diol-containing bis-carbonates. Chapter 4 describes the extension of this methodology to the formation of azacyclic products. This built upon foundation work conducted by a Part II student within the group, and further improved the selectivity of the reaction. Two diverse azacyclic skeletons could be formed from the same substrate by the employment of different bidentate phosphine ligands, and a variety of substrates were examined under these conditions. Chapter 5 draws general conclusions and sets out possible future directions for the methodology, and full experimental details are outlined in Chapter 6.
28
Vincent-Rocan, Jean-François. "N-Isocyanates : Versatile Intermediates in Heterocyclic Synthesis." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34864.
Full textAbstract:
Nitrogen heterocycles are present in nearly 60% of all small-molecule drugs approved by the US Food and Drug Administration. New innovative methods that streamline the synthesis of such heterocycles are therefore highly desirable. The use of new or underdeveloped reactive intermediates provides an excellent opportunity to develop novel heterocyclic syntheses. For example, nitrogen-substituted isocyanates (N-isocyanates) are a class of rare amphoteric isocyanates with high, but severely underdeveloped synthetic potential. The research efforts presented in this thesis have been directed towards the use of such intermediates for the rapid construction of heterocycles using cascade reactions. Using an in situ generation approach from masked (blocked) isocyanate precursors, we were able to control the homo dimerization of these species and design several cascade reactions forming more than 10 different classes of heterocycles using appropriate nitrogen nucleophiles. Given the importance of the N-N-C=O motif in pharmaceuticals and agrochemicals, N-isocyanates provide the opportunity to synthesize highly desirable cores for different industrial applications.
To illustrate the potential of this new tool in heterocyclic chemistry, more than 200 heterocycles were synthesized using this methodology. In Chapter 2, heterocycles incorporating only one atom from the N-isocyanate will be presented. More precisely, the first cascade reaction involving N-isocyanates for the rapid synthesis of saturated heterocycles will be presented. The incorporation of 2 atoms within the ring will then be discussed in Chapter 3 with the synthesis of hydantoins, imidazolones, thiazolines, pyrazoles and phthalazinones. Chapter 4 will focus on the incorporation of every atom in the heterocycle to form other bioactive cores such as azauracils, pyridazinones and azadiketopiperazines. Lastly, Chapter 5 will describe our efforts for the synthesis of acyclic molecules such as semicarbazides and aza-peptides.
29
Murphy, Thomas S. "Time-resolved spectroscopic studies of reactive intermediates." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/31288/.
Full textAbstract:
Chapter 1. Introduction. An introduction to the detection of reactive intermediates by various spectroscopic techniques is given, as well as a brief introduction to perfluorinated solvents, which are used throughout the work presented in Chapters 2 to 4. Chapter 2. Time-Resolved Studies of Spin-Forbidden Reactions of Transition Metal Carbonyls with Weak Ligands. The photolysis of a series of first-row transition metal carbonyl compounds which have been previously reported to form 16-electron coordinatively unsaturated intermediates was examined in a series of perfluorinated solvents using TRMPS (time-resolved multiple probe spectroscopy) and TRIR (time-resolved infrared) spectroscopy. In the case of Fe(CO)5, CpMn(CO)3, (MeCp)Mn(CO)3 and CpV(CO)4, the rate of reaction of the 16-electron intermediate with the perfluorinated solvent was found to be slower than that previously reported for weakly coordinating solvents (e.g. alkanes). Addition of cyclopentane, CO2, Xe and C2H6 to a solution of CpMn(CO)3 in perfluoro(methylcyclohexane) was shown to change the rate of this spin-forbidden reaction, as well as the (CO) band positions of the resulting 1CpMn(CO)2X (X = solvent or dopant) complex. Other perfluorinated materials (perfluoro(hexanes) and perfluoro(triethylamine)) are also shown to allow formation of such weakly-coordinated alkane and noble gas complexes in room-temperature liquid solution. Chapter 3. Further Time-Resolved Studies of Alkane and Noble Gas Complexes in Room Temperature Perfluoroalkane Solutions. The photochemistry of various model transition metal compounds in perfluoroalkane solutions was examined with TRMPS and TRIR spectroscopy. 266 nm photolysis of CpRe(CO)3, Cp*Re(CO)3 and CpRe(CO)2(N2) in perfluoro(methylcyclohexane) solution was found to result in the formation of two distinct dicarbonyl species of the form CpRe(CO)2X, the first of which decay completely on the nanosecond timescale to form the second. The rate of formation, rate of decay and (CO) band positions of this second dicarbonyl species were found to be dependent on the nature of the the solvents or dopants including Xe or cyclopentane present in solution. Similar results were observed for complexes of the form M(CO)6 (M = Cr, Mo, W). DFT calculations were used in conjunction with spectroscopic studies to attempt to confirm the structure of the initially formed species following photolysis of CpRe(CO)3 and M(CO)6 in PFMCH solution. Good agreement was observed between the calculated (CO) band positions of coordinatively unsaturated species and the unknown initially formed CO loss species. Doping of CH4 or C2H6 into a solution of CpRe(CO)3 or Cp*Re(CO)3 resulted in observation of a C-H activated alkyl hydride complex, with the amount of observed C-H activation vaying in the order: CpRe(CO)3 with ethane < Cp*Re(CO)3 with ethane < CpRe(CO)3 with methane < Cp*Re(CO)3 with methane. Photolysis of CpRh(CO)2 in perfluoroalkane solvents was shown to lead to formation of a monocarbonyl solvent complex, followed by the dimeric species Cp2Rh2(CO)3, as well as another species, very tentatively assigned to a C-F activated oxidative addition product. Addition of Xe to the above solution was shown to slow formation of the dimeric species, with no evidence of C-F activation observed, indicating formation of CpRh(CO)Xe in room temperature solution. Chapter 4. Time-Resolved Spectroscopic Studies of Organometallic Triethylsilane Complexes. TRMPS studies of CpMn(CO)3, CpRe(CO)3 and Cp*Re(CO)3 were undertaken in neat HSiEt3 solvent. Photolysis of CpMn(CO)3 resulted in initial formation of 3CpMn(CO)2, following by both direct and indirect formation of the Si-H activated speciesin both cases. Photolysis ofW(CO)6 was found to result in initial formation of the ethyl-boundW(CO)5(EtSiHEt2), which interconverted to form the Si-H-bound speciesW(CO)5(H−SiEt3). Preliminary time-resolved x-ray absorption fine structure spectroscopic studies are also presented. Photolysis of W(CO)6 and CpRe(CO)3 in neat HSiEt3 was observed to cause subtle changes in the absorption edge compared to ground state XAFS spectra, indicating possible formation of transient species in both cases. Chapter 5. Experimental. The experimental techniques utilised in this Thesis are described.
30
Coldren, William Henry. "Theoretical Studies of Reactive Intermediates in Complex Reaction Mechanisms." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531497707269833.
Full text
31
Thompson, John William. "Electronic structure of reaction intermediates and other species." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258013.
Full text
32
Mckelvey, Graham Neil. "Generation and reactions of thionitroso and thioxophosphine intermediates." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/5324/.
Full textAbstract:
A series of alkylthionitroso compounds have been generated via thermal fragmentation of N-chlorothio-N-trimethylsilylalkylamines and intercepted with dienes to form 1,2-thiazine heterocycles (via Diels-Alder reaction) and N-alkylsulfenamides (via Ene reaction). Both types of product were found to be unstable, decomposing in ca. 5h (at 20ºC). The reaction of these thionitroso compounds with dienes was temperature dependant, higher temperature (e.g. 90ºC) favoured the Ene pathway whilst lower temperature (e.g. 50ºC) favoured the Diels-Alder route.Thionitroso compounds 125a-e involving 1,5 and 1,6 S-O or S--S nonbonded interactions were generated and reacted with 2,3-dimethyl-1,3-butadiene to afford 1,2-thiazines 126a-e via Diels-Alder reaction. Compounds 126a-e exhibited remarkable chemical stability relative to 1,2-thiazines without such a nonbonded interaction. This enhanced stability was thought to arise due to the prevention of ring opening by the aforementioned interaction. Low temperature (^1)H NMR and Nuclear Overhauser Enhancement spectroscopy provided physical evidence for the existence of the nonbonded interaction in compounds 126. Reaction of thionitroso compounds with dienes in the presence of metal fluorides (AgF, CsF, KF) resulted in a promotion of the Diels-Alder reaction at the expense of the Ene reaction. When unsymmetrical dienes (1 -methyl-1,3-butadiene, 2-methyl-1,3-butadiene) were used a dramatic increase in the regioselectivity of the cycloaddition reaction was observed. Arylthioxophosphines have been generated, by magnesium induced dechlorination of arylthiophosphonic dichlorides, and intercepted with unsymmetrical dienes (1-methyl-1,3- butadiene, 2-methyl-1,3-butadiene) to afford 1,2-thiaphosphorin heterocycles. The reactions were found to proceed with complete regioselectivity in favour of the C6 and C5 methyl isomers respectively.
33
Hadden, Mark. "Enamides and enaminones : versatile intermediates for heterocycle formation." Thesis, Queen's University Belfast, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322956.
Full text
34
Reynolds, C. A. "Quantum chemical studies of intermediates in nitrosamine carcinogenesis." Thesis, University of St Andrews, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373043.
Full text
35
Johnson, Frank P. A. "Intermediates and excited states of transition metal carbonyls." Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335483.
Full text
36
Munoz, Dulce M. "Synthetic studies on putative intermediates of colletodiol biosynthesis." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341508.
Full text
37
Eypper, Marie. "Photoionisation studies of reactive intermediates with synchrotron radiation." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/191337/.
Full text
38
Patel, Bhaven. "Peri-substituted dithianaphthalenes as sources of reactive intermediates in organic chemistry." Thesis, University of Birmingham, 2009. http://etheses.bham.ac.uk//id/eprint/459/.
Full textAbstract:
This thesis reports the application of 1,8 dithianaphthalenes (peri-substituted dithianaphthalenes) as sources of, and as a means of stabilising, reactive intermediates in organic chemistry. Three peri-substituted trisulfide-2-oxides (49, 58 and 103) were prepared by reacting 1,8-naphthalene dithiols with thionyl chloride in the presence of pyridine. The trisulfide-2-oxides 49, 58 and 103 were shown to act as sulfur monoxide transfer reagents with dienes. ortho-Substituents on the naphthalene ring increased the rate and lowered the temperature at which SO transfer occurred. Treatment of the resulting sulfoxides under Pummerer conditions afforded the corresponding thiophenes. SO transfer was applied in a formal synthesis of Plavix® and the naturally occurring thioperillene. Mechanistic studies on the SO transfer reaction indicated that the rate-determining step was independent of the diene, and first-order with respect to trisulfide-2-oxide. C-H abstraction from cycloheptatriene suggested formation of triplet SO. vic-Disulfoxides are reactive intermediates in the oxidation of thiosulfinates to thiosulfonates. The oxidation of 1,8-naphthalene disulfides was investigated. Cyclic voltammetry demonstrated that electron-rich 3,8-dimethoxynaphtho[1,8-cd][1,2]dithiole (87) was easier to oxidise than the parent naphthalene disulfide 50. Treatment of 87 with one equiv. of oxidant resulted in formation of thiosulfonate 206 and disulfide 87, suggesting disproportionation of thiosulfinate 205. Oxidation of t-Bu-substituted disulfide, 3,8-di-tert-butylnaphtho[1,8-cd][1,2]dithiole (65), afforded the isolable trans vic-disulfoxide 217. Isomerisation of 217 occurred thermally and photochemically, generating cis vic-disulfoxide 225 and thiosulfonate 224. Complete rearrangement of 217 to the thiosulfonate 224 occurred in refluxing mesitylene, establishing trans-217 as the most stable vic-disulfoxide to date. Bis(sulfonyl)hydroxylamine 284 is proposed as a potential source of nitric oxide (NO) or nitroxy (HNO). 284 was prepared by formal N-insertion into the S(O)-S(O)\(_2\) bond of sulfinyl sulfone 228, prepared in turn through oxidation of disulfide 50. Bis(sulfonyl)hydroxylamine 284 was found to be stable both thermally and photochemically. Investigations into the oxidation of t-Bu-substituted disulfide resulted in the isolation of sulfinic anhydride, 295, from disulfide 65. Desulfonylation occurred when 295 was heated in H\(_2\)O/1,4-dioxane. Deuterium incorporation occurred on running the reaction in D\(_2\)O/1,4-dioxane. Refluxing 295 in PhCl resulted in deoxygenation to disulfide 65.
39
Whittle, Carl. "Fundamental Investigations of Mechanistic Pathways of Selected Organic Reactive Intermediates." TopSCHOLAR®, 1997. http://digitalcommons.wku.edu/theses/360.
Full textAbstract:
Part 1 of this thesis deals with the role that it -electron density plays in the formation of it -complexes in electrophilic aromatic substitution. Using commercial and synthetic compounds of varying it-electron density, the fact that % -complexes actually exist in these species was determined by a mass spectral investigation that was designed to monitor alkyl side-chain isomerizaitons. Also, the amount of it-complex was determined for each compound by measuring the amount of alkyl carbenium ion loss in each compound's mass spectrum. Found within the systems was an internal trend showing that the greater the amount of 7t-electron density in the ring, the less it-complex formed. This trend was further studied utilizing a Spartan 3.0 computational system, and all data found was internally consistant with the experimental data. It was found that the compounds with the greatest nelectron density used the excess tc-electron density for greater covalency in the complex. In Part 2, the gas-phase reaction between the ethylene oxide radical cation and neutral ethylene oxide, when performed in the high-pressure source of a tandem mass spectrometer, forms a C4Hg02 radical cation adduct. The collisionally activated dissociation (CAD) mass spectrum of the C4H802 adduct is nearly identical to that of the 1,4-dioxane radical cation. Computational investigations utilizing semi-empirical AMI, MNDO, and PM3 methodologies were invoked to determine the mechanistic pathways involved in the reaction. The most likely mechanism is a step-wise process involving a long-chain distonic radical cation intermediate that subsequently forms a non-distonic cyclic radical ion. A calculated thermodynamic driving force of ca. 10 Kcal/mol exists for the cyclization of the long-chain distonic radical cation. For Part 3, an array of acyclic long-chain distonic radical cations was generated and analyzed by semi-empirical AMI computational methods. In general, an enthalpic driving force for the isomerization of the distonic ions to cyclic non-distonic ions was observed. The enthalpies of the isomerizations were evaluated as a function of chain length, identity of the atom (C, O, N) bearing the radical site, and substitution of the radical and carbenium ion sites. The structures, electron distribution, free spin distribution, and thermodynamic stabilities of the cyclic ions generated upon isomerization of the distonic ions were nearly identical to those formed by direct removal of an electron from the corresponding cyclic neutral precursor.
40
Caulkins, Bethany Gayle. "Enzymatic Intermediates of Tryptophan Synthase at Atomic Resolution Using Solid-State NMR." Thesis, University of California, Riverside, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10286555.
Full textAbstract:
The acid-base chemistry that drives catalysis in pyridoxal-5'-phosphate (PLP)-dependent enzymes has been the subject of intense interest and investigation since the initial identification of its role as cofactor in this extensive class of enzymes. X-ray crystallography, optical spectroscopy, and physical-organic studies point to the importance of protonation/deprotonation at ionizable sites on the coenzyme, substrates, and sidechains to activate key steps in the catalytic process. Yet direct characterization remains elusive as these techniques cannot specifically identify proton locations or report unambiguously on local chemical environment. The chemical shift in nuclear magnetic resonance (NMR), however, is an extremely sensitive probe of chemical environment, but a large complex like a protein will give an enormous amount of data that can be inscrutable without guidelines for specific structure determination. The use of computational chemistry aids in the creation of models that rely on specific chemical-level details and predicts detailed information like chemical shift. We employ NMR crystallography – the synergistic combination of X-ray diffraction, solid-state NMR spectroscopy, and computational chemistry - to define three-dimensional, chemically-detailed structures of the intermediates in the tryptophan synthase cycle under conditions of active catalysis. Together these methods can provide consistent and testable models for structure and function of enzyme active sites. Our results from studies on tryptophan synthase confirm some long-held mechanistic hypotheses, but also point to several novel structural hypotheses.
41
Kline, Neal. "Moderate Resolution Cavity Ringdown Spectroscopy of Reactive Intermediates Relevant to Hydrocarbon Oxidation." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1405979077.
Full text
42
Clark, Peter David. "Synthesis of drug intermediates in carbon dioxide." Thesis, University of Nottingham, 2007. http://eprints.nottingham.ac.uk/11912/.
Full textAbstract:
The application of supercritical C0₂(scC0₂) as a solvent for the synthesis of fine and bulk chemicals has been well documented; however its application as a solvent for the synthesis of pharmaceuticals is yet to be exploited fully. To address this issue, two synthetically important reactions have been investigated in scC0₂; chemoselective N-debenzylation and diastereoselective hydrogenation. Chapter 3 details the study of catalytic N-debenzylation in the presence of sensitive functional groups (COMe and Cl). It has been shown that selective N-debenzylation in the presence of a carbonyl (COMe) is difficult to achieve due to the high operating temperatures that are required to facilitate continuous flow debenzylation. N-debenzylation in the presence of chloro- substituents was also investigated. Dechlorination can be a major problem during this reaction however several different strategies were developed to suppress dechlorination including: (i) the correct selection of catalyst support; (ii) selective poisoning of a Pd catalyst; (iii) the addition of acids, such as H₂S0₄ to the reactant stream; (iv) the use of an aprotic co-solvent, such as THF. Chapter 4 covers progress made on the diastereoselective hydrogenation of the pharmaceutical intermediate, rac-sertraline imine. It has been shown that the hydrogenation reaction can be performed with excellent levels of chemo- and diastereoselectivity (cis:trans ratio of 97:3, 0.7 % by-product formation) by performing the reaction as a continuous flow process in the presence of scC0₂ All details of the apparatus, experimental and synthetic procedures are reported in Chapter 2.
43
Gregory, Alexander William. "Cyclisation cascades via reactive iminium intermediates." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:8e633fee-3457-4c31-939c-4421fac2fb8f.
Full textAbstract:
The aim of this D.Phil was to develop a range of cyclisation cascades, which initially form a reactive iminium intermediates that can then be attacked by a pendant nucleophile resulting in novel polycyclic structures. This concept has been applied to the development of three methodologies and has resulted in the discovery of new reactivity as well as the synthesis of a wide range of interesting novel structures Chapter 1: Enantioselective chiral-BINOL-phosphoric acid catalysed reaction cascade A highly enantioselective hydroamination / N-sulfonyliminium cyclisation cascade using a combination of Au(I) and chiral phosphoric acid catalysts has been developed. Proceeding by an initial 5-exo-dig hydroamination and a subsequent phosphoric acid catalysed Pictet- Spengler cyclisation, the reaction provides access to complex sulfonamide scaffolds in excellent yields and with high levels of enantiocontrol. The scope can be extended to lactam derivatives, with excellent yields and enantiomeric excesses of up to 93% ee. Chapter 2: Iridium catalysed nitro-Mannich cyclisation A new chemoselective reductive nitro-Mannich cyclisation reaction sequence of nitroalkyltethered lactams has been developed. An initial rapid and chemoselective iridium(I) catalysed reduction of lactams to the corresponding enamine is subsequently followed by intra molecular nitro-Mannich cyclisation. This methodology provides direct access to important alkaloid, natural product-like structures in yields up to 81% and in diastereoselectivities that are typically good to excellent. An in-depth understanding of the reaction mechanism has been gained through NMR studies and characterisation of reaction intermediates. The new methodology has been applied to the total synthesis of (±)-epi-epiquinamide in 4 steps. Chapter 3: Iridium catalysed reductive interrupted Pictet-Spengler cyclisation A novel reductive interrupted Pictet-Spengler cyclisation reaction cascade has been created. An iridium(I) catalyzed partial reduction of lactams/amides to the corresponding iminium is subsequently trapped by a pendant indole nucleophile. Interruption of the Pictet-Spengler reaction by indolium reduction provides a wide range of novel spirocyclic indoline moieties in excellent yield and diastereoselectivity.
44
Graham, Alan. "Carbanion and enol intermediates in c-nitrosation and halogenation." Thesis, Durham University, 1991. http://etheses.dur.ac.uk/6039/.
Full textAbstract:
A kinetic study of the mtrosation of ethyl cyanoacetate, diethyl malonate and malononitrile, in acidic water/dioxan solution, by nitrous acid, at 25ºC, was under taken. Catalysis of this reaction was obtained by the addition of nucleophilic catalysts; chloride ion, bromide ion, thiocyanate ion and thiourea. The results were consistent with a mechanism where malononitrile reacted exclusively via the carbanion intermediate. Within the pH range used, pH 0∙7 to pH 3∙3, ethyl cyano acetate and diethyl malonate reacted either through a carbanion intermediate, at higher acidity, or an enol intermediate, at lower acidity. Values of the second order rate constant for the attack of the nitrosating species upon the carbanions were obtained. The carbanions of malononitrile and diethyl malonate reacted at the diffusion limit, in the presence of catalysts. Nitrosation of ethyl cyanoacetate, via its carbanion, showed an already established trend in the reactivity of the nitro sating species, NOSC(NH(_2))(_2) < NOSCN < NOBr < NOCl. A kinetic study of the nitrosation of malonic and methylmalonic acids, and of the iodination and bromination of these two acids as well as ethylmalonic and phenylmalonic acids, in aqueous acidic solutions, at 25ºC, was also undertaken. At high acidity nitrosation was shown to proceed via an enol intermediate and at lower acidities via a carbanion. Nitrosation of the intermediate was rate determining. Under certain conditions, in nitrosation, it was possible to make the enolisation rate limiting. lodination and bromination, by the halogen molecules, involved rate determining enol formation. lodination by triiodide ion involved rate determining iodination of the enol. Values of the enolisation rate constant, kg, were obtained for all four of the acid substrates, these were in reasonable agreement for the different electrophilic processes. Between pH 0 and pH 2 the results fitted an intramolecular acid catalysed enolisation mechanism. At higher pH values (2 to 4) the results fitted a change in mechanism to include, additionally, base catalysed enolisation and enol carboxylate formation pathways.
45
Burger, Ryan. "Efficient manufacture of emulsion intermediates in cavity-design mixers." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2039579/.
Full textAbstract:
Emulsions are ubiquitous across the process industries and are often utilised in applications where controlled delivery of a key ingredient (e.g. an oil or water soluble compound) is an important consideration. Their functional properties e.g. the rate of absorption or coverage of a surface is generally determined by the size and size distribution of dispersed domains or microstructure. Control over the formulation, process route and type of equipment all influence the resulting microstructure. The focus of this thesis is the development of process strategies for the efficient manufacture of emulsions in novel cavity-design mixers utilising the Controlled Deformation Dynamic Mixer (CDDM). The CDDM comprises a cylindrical rotor-stator design with opposing surfaces with embedded cavities. The novel design allows flexible operation and optimisation across the spectrum of process space, defined by dispersive and/or distributive mixers. The process strategies are empirically demonstrated across several oil/surfactant types and the impact of emulsion composition, mixer geometry and process methods are studied. The resulting emulsions are assessed via light scattering measurement of the droplet domain sizes and interfacial areas. The link between microstructure and product viscosity is discussed. An important output of this work was the development of an emulsification efficiency parameter. The parameter provides a useful analytical tool for evaluating the process strategies and is used to provide insights into how the implementation of the in-line emulsification of high internal phase emulsion strategies could provide commercial opportunities via emulsifier raw materials saving and development of small footprint processes.
46
Zhang, Hu. "Engaging Chiral Cationic Intermediates by Anion-Binding in Asymmetric Catalysis." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:26718738.
Full textAbstract:
Anion-binding catalysis by dual hydrogen-bond donors such as ureas and squaramides has been demonstrated as a powerful strategy for the development of highly enantioselective transformations involving prochiral cationic intermediates, such as iminium ions, oxocarbenium ions, carbenium ions, and episulfonium ions. The research described in this dissertation explores the ability of dual H-bond donor catalysts to engage chiral cationic intermediates and to induce enantioselectivity in transformations involving such intermediates.
In Chapters 1, we provide an overview of the progress and challenges in the development of enantioselective halo- and seleno-functionalization reactions, which proceed via three-membered ring cationic halonium or seleniranium ions.
In Chapter 2, we report a highly enantioselective selenocyclization reaction that is promoted by the combination of a chiral squaramide catalyst, a mineral acid, and an achiral Lewis base. Mechanistic studies reveal that the enantioselectivity originates from the dynamic kinetic resolution of seleniranium ions through anion-binding catalysis.
Chapter 3 details our discovery of a squaramide-catalyzed enantioselective iodoisocyanation reaction, which represents a rare example in asymmetric intermolecular halofunctionalization of simple olefins. Kinetic studies reveal that [I(NCO)2]–1 anion is the counterion of iodonium intermediate and the dual H-bond donor catalyst aggregates in the resting state. Hammett analysis indicates that the degree of stabilization by catalyst to the iodonium intermediate accounts for both catalysis and enantioselectivity.
The reactions developed in Chapter 2 and 3 have therefore extended anion-binding catalysis to reactions involving chiral and stereochemically labile halonium and seleniranium cations. Knowledge learned in these studies will provide valuable guidance to the development of asymmetric transformations involving other chiral cationic intermediates.Chemistry and Chemical Biology
47
Zhu, Rong Ph D. Massachusetts Institute of Technology. "Development of copper-catalyzed enantioselective alkene difunctionalization reactions via radical intermediates." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97988.
Full textAbstract:
Thesis: Ph. D. in Organic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2015.Cataloged from PDF version of thesis. Vita.
Includes bibliographical references.
Chapter 1 A mild, versatile, and convenient method for the efficient oxytrifluoromethylation of unactivated alkenes based on a copper-catalyzed ligand-assisted difunctionalization strategy has been developed. This method provides access to a variety of classes of synthetically useful CF3-containing building blocks from simple starting materials. Chapter 2 A method for the efficient enantioselective oxytrifluoromethylation of alkenes has been developed using a copper catalyst system inspired by the ligand dependence observed in the racemic reaction. Mechanistic studies are consistent with a metal-catalyzed redox radical addition mechanism, in which a C-0 bond is formed via the copper-mediated enantioselective trapping of a prochiral alkyl radical intermediate derived from the initial trifluoromethyl radical addition. Chapter 3 A general and versatile method for the catalytic enantioselective oxyfunctionalization of alkenes has been developed based on a key Cu-mediated enantioselective C-0 bond forming process of prochiral alkyl radical intermediates. A wide range of radicals were found to participate this type of reaction, including azidyl, arylsulfonyl, aryl, acyloxyl and alkyl radicals. This method provides rapid access to a broad spectrum of interesting enantiomerically enriched lactones through tandem C-N/C-O, C-S/C-O, C-Cary/aIkyI/C-O or C-O/C-O bond formation, in good yields and enantiomeric excesses with good functional group compatibility.
by Rong Zhu.
Ph. D. in Organic Chemistry
48
Turner, Jack. "Time resolved infrared studies of reactive intermediates." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/50153/.
Full textAbstract:
Chapter 1: Introduction This Chapter provides an introduction to the study of reactive intermediates and the specialised techniques which have been developed in order to study these extremely short lived species. In particular, it provides an overview of ultrafast Time Resolved Infrared Spectroscopy (TRIR). This key technique underpins a large amount of the work presented in this Thesis as well as a description of the apparatus and methods used across the other Chapters of this Thesis. Chapter 2: Ultrafast TRIR studies of rhenium complexes of thioether substituted hexaazatrinapthylene ligands The excited states and photophysical properties of mono, bi and trinuclear (Re(CO)3Cl) complexes of the 2,3,8,9,1314-hexa (octyl-thioether)-1,6,7,12,13,18-hexaazatrinapthylene ligand (HATN-S(C8H17)6) have been investigated using ultrafast TRIR spectroscopy. These measurements are supported by theoretical calculations and resonance Raman spectroscopic investigations of these compounds. The position and the intensity of the (CO) bands of the photoexcited species directly report on the electron transfer/distribution in the excited state. In all cases the observed product bands were blue shifted compared to the parent, this is consistent with electron transfer away from the metal centre. The observed shift for the thioether substituted HATN complexes studied here was smaller than that reported for the analogous HATN-Me6 complexes, indicating reduced electron transfer upon excitation. Red shifted product bands corresponding to “spectator” metal centres were also observed for the bi and trinuclear species, these bands were shifted by approximately the same amount as for the HATN-Me6 species, indicating a similar reduction of the HATN core upon excitation. These results are consistent with the formation of a dual charge transfer ILCT/MLCT excited state involving electron donation from both a metal centre and the thioether moieties upon excitation. Chapter 3: Ultrafast TRIR studies of rhenium and platinum complexes of Pyridyl-1,2,3-Triazole and related ligands The excited states and photophysics of a series of substituted rhenium and platinum complexes that contain a 2-pyridyl-1,2-3-triazole ligand, an easily modified analogue of the common 2,2’-bipyridine (bpy)ligand, have been studied by TRIR spectroscopy. The compounds are found to be analogous of similar complexes with bpy, exhibiting MLCT or MLLCT exicted states (in the case of the (Re(CO)3X) and (Pt(CCHPh)2) complexes respectively). Changing the substitution of the triazole ring has little effect on the excited state band positions, this is attributed to the insulating effect of the triazole moiety. Complexes substituted with conjugated phenyl groups on the triazole ring exhibit greatly increased excited state lifetimes than those substituted with non-conjugated benzyl groups. This is attributed to the rigid rotor effect. The addition of an electron donating triphenylamine group to the pyridyl moiety results in the observation of ILCT states. Chapter 4: Towards long lived alkane and noble gas complexes from cationic piano stool complexes in the fluorous phase The synthesis and characterisation of a series of cationic transition metal tricarbonyl half sandwich complexes solubilised in perfluoroalkane solvents by means of the weakly coordinating, fluorous solubilising anion tetrakis(3,5-bis(perfluorohexyl)phenyl)borate (BArF64) is described. These complexes were photolysed in perfluoroalkane solutions doped with methane, heptane and xenon and followed by ultrafast TRIR spectroscopy with the aim of generating long-lived organometallic alkane and noble gas complexes suitable for study by NMR at room temperature. While no organometallic alkane or noble gas complexes were observed, several novel transition metal-BArF64 zwitterionic species are generated upon photolysis. These species are the result of -2 binding of one of the aryl moieties of the BArF64 anion to the vacant coordination sites generated following photoejection of a carbonyl ligand. While highly reactive they are long lived and appear to be permanent photoproducts. In the case of the rhenium complex an additional product band assigned as a dimeric species is also observed. Chapter 5: Towards the synthesis of fluorous phase soluble cationic piano stool complexes. The synthesis of fluorous tagged cationic transition metal tricarbonyl complexes is explored with the eventual aim of performing fluorous phase TRIR experiments utilising the more weakly coordinating (but less solubilising) anion tetrakis(perfluoro-tert-butoxy)aluminate in place of the previously studied BArF64 anion. Several routes to perfluoroalkyl arene ligands are explored and evaluated, as is the use of different lengths of alkyl spacer to insulate the ligand binding site from the strong electron withdrawing effects of the perfluoroalkyl moiety. This process lead to the synthesis of the new complexes [(m-(3-(perfluorooctyl)-propyl)n-benzene)manganesetricarbonyl] hexafluorophosphate for n =1-3. These compounds are soluble in the fluorous phase despite their charge. The use of the m-(3-(perfluorooctyl)-propyl)n-benzene ligand to solubilise complexes of rhenium and rhodium was also attempted. The addition of methyl groups to the ring was explored as a route to additional steric bulk and a more electron rich, strongly binding ligand. In addition to arenes, the fluorous tagging of other ligand systems was also investigated, including cyclopentadienyl and tris(1-pyrazolyl)methane.
49
Groarke, Michelle J. "Synthesis of novel heterocycles from amino acids via diazocarbonyl intermediates." Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322957.
Full text
50
McCarthy, Noreen. "Catalytic asymmetric synthesis and homochiral transformations using #alpha#-diazocarbonyl intermediates." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333843.
Full text