Log in

Relevant bibliographies by topics / Ring formation / Dissertations / Theses

To see the other types of publications on this topic, follow the link: Ring formation.

Dissertations / Theses on the topic 'Ring formation'

Author: Grafiati

Published: 4 June 2021

Last updated: 19 February 2023

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles

Select a source type:

Consult the top 50 dissertations / theses for your research on the topic 'Ring formation.'

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

Olmsted, Susan C. "Star Formation in Ring Galaxies." Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/honors/322.

Full text

Abstract:

Ring galaxies are specific types of interacting galaxies in which a smaller galaxy has passed through the center of the disk of another larger galaxy. The intrusion of the smaller galaxy causes the structure of the larger galaxy to compress as the smaller galaxy falls through, and to recoil back after the smaller galaxy passes through, hence the ring-like shape. In our research, we studied the star-forming regions of a sample of ring galaxies and compared to those of other interacting galaxies and normal galaxies. Using UV, optical, and IR archived images in twelve wavelengths from three telescopes, we analyzed samples of star-forming regions in ring and normal spiral galaxies using photometry. To measure the star formation rates of the star forming regions, we used computer software that picked out the regions and measured their luminosities in all twelve wavelengths, before comparing the luminosities in these wavelengths to determine the rate of star formation. We have determined that ring galaxies have proportionally more clumps with higher star formation rates than spirals, and a similar trend was suggested when comparing ring galaxies to other interacting galaxies (though more data is required for that comparison). These findings can help us understand galaxy evolution, including the evolution of our own galaxy.

APA, Harvard, Vancouver, ISO, and other styles

2

Sutton, Phil J. "Saturn's turbulent F ring." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/18475.

Full text

Abstract:

As our abilities to utilise high performance computing to theoretically probe many astrophysical systems increases, a genuine need to relate to real systems becomes ever more important. Here, Saturn s rings can be used as a nearby laboratory to investigate in real time many astrophysical processes. One such system is the narrow F ring and its interaction with its inner shepherd moon Prometheus. Through numerical modelling and direct observations of the in-situ spacecraft Cassini we find new and exciting dynamics. These might help explain some of the asymmetries witnessed in the distribution of embedded moonlets and azimuthal ring brightness known to exist within the F ring. Spatially we find asymmetry in the Prometheus induced channel edges with regards to density, velocity and acceleration variations of ring particles. Channel edges that show fans (embedded moonlets) are also the locations of highly localised increases in densities, velocity and acceleration changes where opposing edges are considerably less localised in their distribution. As a result of the highly localised nature of the velocity and acceleration changes chaotic fluctuations in density were witnessed. However, this could seek to work in favour of creating coherent objects at this channel edge as density increases were significantly large. Thus, density here had a greater chance of being enhanced beyond the local Roche density. Accompanied with these dynamics was the discovery of a non-zero component to vorticity in the perturbed area of the F ring post encounter. By removal of the background Keplerian flow we find that encounters typically created a large scale rotation of ~10,000 km^2. Within this area a much more rich distribution of local rotations is also seen located in and around the channel edges. Although the real F ring and our models are non-hydrodynamical in nature the existence of a curl in the velocity vector field in the perturbed region could offer some interesting implications for those systems that are gas rich.

APA, Harvard, Vancouver, ISO, and other styles

3

Hylands, Kevin Alexander. "Nitrate ester formation from small ring heterocycles." Thesis, University of Exeter, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337731.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Harter, Braxton Nicholas. "Lagrangian Coherent Structures in Vortex Ring Formation." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1565828293505214.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Robertson, Jeremy. "Ring expansion reaction via homolytic pathways." Thesis, University of Oxford, 1990. http://ora.ox.ac.uk/objects/uuid:194ca194-4848-470b-a21f-c16869257b96.

Full text

Abstract:

The preparation of carbocyclic medium rings by two electron processes is reviewed with particular reference to the synthesis of natural products. The formation of medium rings by oxidative and homolytic methods is also reviewed. The synthesis and behaviour of both cis- and tran- ring expansion precursors is described. The 1,4-addition of tributylstannyl lithium to a range of cyclic α,β-unsaturated ketones was performed and procedures found whereby the so-formed enolates could be alkylated with a variety of electrophiles. Using these procedures a range of trans- ring expansion precursors were obtained in moderate to good yield. By the 1,4-addition of tributylstannyl lithium to 2-(ω-phenylselenoalkyl)-cyclohexenones, followed by enolate quenching with either water or methyl iodide, a range of cis- ring expansion precursors were produced. Homolytic ring expansion by either one, three, or four carbon atoms was shown to be possible, producing, respectively, seven, nine, or ten membered functionalised cycloalkenones in high yield except in cases where intramolecular reductive elimination was also possible. Attempts to extend this methodology to the synthesis of exomethylene cycloalkanones is described. The 3-tributylstannyl-3-(ω-phenylselenoalkyl)-cyclohex-2-enone precursors were found not to be successful substrates for ring expansion. The regiospecific alkylation of 2-(tributylstannylmethyl)-cyclohexanone with l-chloro-4-iodo-butane, followed by conversion of the chloride moiety to iodide led to a precursor which, on exposure to homolysis conditions, fragmented to produce the desired exomethylene cyclodecanone in high yield. Work directed towards the synthesis of medium ring cycloalkynones is described. Procedures were developed whereby 2-alkylated cyclohexan-l,3-dione derivatives could be obtained cleanly and in excellent yield on a large scale. The conversion of these derivatives to potential cycloalkynone precursors is described. It is shown that the products obtained after exposure of these precursors to homolysis conditions could, in principle, be derived from the putative cycloalkynones and mechanisms are suggested to explain the formation of these compounds. The homolytic ring expansion reaction was also performed on a substrate possessing an acyl radical precursor in the hope that a medium ring 1,2-dione would be produced. The synthesis of this substrate and its behaviour towards ring expansion is described. It is shown that, again, radical reaction was successful (to the medium ring dione) however subsequent reactions of this product led to the isolation and characterisation of a number of compounds . Attempts to extend this methodology to the synthesis of the natural products curdione and neocurdione is also described. Model reactions with 2,6-dimethylcyclohex-2-enone as the 1,4-addition precursor and 1,4-di-iodobutane as the electrophile led to a ring expansion substrate which fragmented to two ring contracted isomeric compounds in addition to the ring expanded material. Approaches to the preparation of suitable electrophiles for the natural product synthesis are described and their proposed use in subsequent conversion to curdione and neocurdione given.

APA, Harvard, Vancouver, ISO, and other styles

6

Tigges, Sophia E. "The relationship between Centaur activity and ring formation." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115778.

Full text

Abstract:

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 22-25).
Introduction: Centaurs are small bodies whose orbits lie between those of Jupiter and Neptune (Gehrels, 1999). They are thought to be transition objects that originate in the Kuiper belt and occupy the cis-Neptunian region before potentially becoming Jupiter-family or other short-period comets (Dones, Levison, & Duncan, 1996). Their short dynamical lifetimes are on the order of 106 years (Horner, Evans, & Bailey, 2004) due to their unstable, planet-crossing orbits (Horner, Evans, Bailey, & Asher, 2003). Some Centaurs have been observed to be active, and the bodies in the population of active Centaurs have perihelion distances that are statistically smaller than the median perihelion distance for all Centaurs, suggesting that Centaur activity is thermal in nature (Jewitt, 2009). Centaur activity may be observed through changes in the brightness of an object such as those exhibited by the Centaur Chiron (Parker et al., 1997). The presence of a coma around a Centaur may also provide evidence of activity, and dust comae have been detected around several bodies including Chiron (Meech & Belton, 1989; Luu & Jewitt, 1990) and Echeclus (Choi, Weissman, & Polishook, 2006). In addition to comae, other structures have been observed around Centaurs, such as the ring system that was discovered around Chariklo during a stellar occultation (Braga-Ribas et al., 2014). A symmetric feature was observed around Chiron during an occultation (Ruprecht et al., 2015), and some interpret this feature to be possible ring material (Ortiz et al., 2015). Similarly, the trans-Neptunian dwarf planet Haumea was revealed to have a ring during a stellar occultation (Ortiz et al., 2017). The collisional spreading time of Chariklo's rings was calculated to be on the order of 101 years, which is short in comparison to the estimated Centaur lifetime of approximately 106 years (Pan & Wu, 2016), yet Centaur rings are still observed despite this contradiction. Shepherd satellites may serve to increase the lifetime of a Centaur's rings (Pan & Wu, 2016) and maintain distinct ring edges such as those observed in Chariklo's ring system (Charnoz, Canup, Crida, Dones, 2017). Moreover, Centaur activity could supply material to an already present ring system, thus prolonging its lifetime. This study explores the potential connection between Centaur activity and Centaur ring systems by using the N-body integrator REBOUND to model outburst particle interactions and distributions.
by Sophia E. Tigges.
S.B.

APA, Harvard, Vancouver, ISO, and other styles

7

Prasad, Chaturvedula V. "Annulation and cycloaromatization reactions of 3-aryl (alkyl) thio-1-trimethylsiloxy-1-methoxy-1,3-butadienes." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75442.

Full text

Abstract:

The title compounds were synthesized from methyl 3-aryl(alkyl)thio crotonic acids by deprotonation followed by silylation. The reactions of dienes with a number of carbonyl electrophiles under Lewis-acid catalysed conditions were investigated. The dienes exclusively give $ gamma$-alkylated products. The thio substituent enhances the $ gamma$-selectivity.
The reactions of dienes with a number of 1,3-dicarbonyl equivalents have been studied and a cycloaromatization reaction has been developed for the regiocontrolled synthesis of aryl sulfides in a 3C + 3C combination. The role of dienes in Diels-Alder reactions has also been investigated.
A new 4C + 2C annulation reaction has been developed based on the propensity of dienes to undergo Michael reaction with $ alpha$,$ beta$-unsaturated ketones under Lewis-acid catalysed conditions. These Michael adducts in turn were cyclized either with potassium tert-butoxide or with lithium thiophenoxide. Further, the tandem Michael-Claisen annulation reaction can be controlled to give either cis- or trans-fused 9-methyldecalin system with three carbonyl groups which are differently masked. The chemoselective transformations of the carbonyl groups were also described.

APA, Harvard, Vancouver, ISO, and other styles

8

Lam, Yan-yu Sarah, and 林恩如. "Studies and applications of intermolecular (4+3) cycloaddition reactions of epoxy and aziridinyl enolsilanes." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/206359.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Schaefer, Anthony G. "Part 1, stereoselection in (4+2) cycloadditions ; Part 2, synthesis of 14-epiupial /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487585645577956.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

Olcay, Ali Bahadir. "Measurement of ambient fluid entrainment and calculation of vortex ring impulse during vortex ring formation." Ann Arbor, Mich. : ProQuest, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3258314.

Full text

Abstract:

Thesis (Ph.D. in Mechanical Engineering)--S.M.U., 2007.
Title from PDF title page (viewed Mar. 18, 2008). Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1890. Adviser: Paul Krueger. Includes bibliographical references.

APA, Harvard, Vancouver, ISO, and other styles

11

Pungente, Michael D. "Antibody-catalyzed formation of a 14-membered ring lactone." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25138.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Giang, Yun-Seng F. (Yun-Seng Frank). "Intramolecular 2+2 Cycloadditions of Ketenes." Thesis, North Texas State University, 1986. https://digital.library.unt.edu/ark:/67531/metadc331159/.

Full text

Abstract:

The objective of this study was to explore intramolecular ketene cycloadditions with the anticipated results of developing new synthetic methodology for the synthesis of polycyclic compounds difficult to obtain by other procedures. (o-Alkenylphenoxy)ketenes were initially selected for this study because these ketenes provided a favorable proximity for the intramolecular [2+2] cycloaddition reactions. The difunctional precursors, (o-alkenylphenoxy)- acetic acids, were readily prepared from o-alkenylphenols and ∝-halocarboxylic acids and were converted to the corresponding acid chlorides by reaction with oxalyl chloride. The acid chlorides were dehydrochlorinated to the corresponding (o-alkenylphenoxy)ketenes by treatment with triethylamine. The ketenes undergo a facile intramolecular [2+2] cycloaddition to give polycyclic eye 1obutanones. The (o-vinylphenoxy)ketenes are clearly more reactive than the (o-allylphenoxy)ketenes and provide much better yields of the cycloaddition products because of electronic effects in the transition state in the cycloaddition process. The intramolecular [2+2] cycloadditions of keteniminium salts were included in this study as a more electrophilic alternative to ketenes that will react with less nucleophilic carbon-carbon double bonds. However, the use of keteniminium salts instead of ketenes in Intramolecular cycloadditions does have some limitations. The synthesis of benzofurans via the intramolecular [2+2] cycloadditions of (o-acylphenoxy)ketenes was accomplished. The initially formed ß-lactone cycloaddition products spontaneously underwent decarboxylation to the benzofurans. The aromaticity of the benzofurans is apparently a very strong driving force for the cycloaddition. During the course of this study, two new synthetic methods were discovered which in many instances represent a significant Improvement over existing methods. The Wittig Reactions of ketoacids without protecting the carboxyl groups provide a reliable source of the precursor unsaturated acids needed for intramolecular ketene-olefin cycloadditions. Also, the one-pot preparation of intramolecular ketene cycloaddition products from the carboxylic acid via the tosylate represents a new synthetic method. This procedure eliminates the acid halide preparation, isolation and purification step, thereby significantly simplifying the synthesis.

APA, Harvard, Vancouver, ISO, and other styles

13

Leftwich, Timothy Ray. "Modification of silicon-based substrates with cyclocondensation and cycloaddition reactions." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 111 p, 2010. http://proquest.umi.com/pqdweb?did=1992491831&sid=7&Fmt=2&clientId=8331&RQT=309&VName=PQD.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Sengpracha, Waya. "Synthesis of biologically active indole-fused heterocyclic derivatives." Department of Chemistry - Faculty of Science, 2005. http://ro.uow.edu.au/theses/279.

Full text

Abstract:

New synthetic routes to 1,2- and 2,3-fused indoles with seven- or eight-membered rings have been developed in this project, with the longer term aim of assessing their biological activity. Approaches to such fused indole derivatives were accessed via free radical cyclisation from 1- or 2-substituted indole derivatives with haloacetamide precursors. Using 1-substituted indole derivatives with haloacetamide functionalites, free radical cyclisation reactions gave fair yields of the indole- and dihydroindole-fused eight membered ring derivatives. Using 2-substituted indole derivatives with haloacetamide functionalities, prepared in turn by a palladium-mediated cyclisation of N-substituted indoles followed by hydrolysis and subsequent decarboxylation, free radical cyclisation afforded the 7,12-dihydro-indolo[3,2-d]benzazepin-6(5H)-one (Paullone) system in fair yields. A novel synthetic approach to a bis-indole fused seven-membered ring system was developed based on an N-substituted spirooxindole rearrangement. The spiro-indolinols obtained from partial amide reduction underwent rearrangement to give the bis-indole fused seven-membered ring derivatives 270 and 271 under acidic conditions. Antimicrobial activity of the indole fused eight-membered ring systems was evaluated. The compound 5,14-dihydro-10-methoxy-5-methoxy-5-methyindolo[2,1-d][1,5]benzodiazocin-6-one 186c showed by far the most potent antibacterial activity (against Staphylococcus aureus), while 5,14-dihydro-5-(4-methoxybenzyl)indolo[2,1-d][1,5]benzodiazocine-6-one 186d showed good in vitro antimalarial activity against both drug resistant and drug sensitive strains of Plasmodium falciparum. These two compounds represent novel structural leads for such activities.

APA, Harvard, Vancouver, ISO, and other styles

15

Barbieri-Arhancet, Graciela I. "New oxy-dihydrofuran annulation methodology." Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-09162005-115038/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Trova, Michael Peter. "Bond shifting and ring inversion within 1,4- and 1,5-annulated cyclooctatetraenes /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487335992904171.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Pulipaka, Aravinda B. "Intramolecular ring opening reactions of aziridines by [pi]-nucleophiles /." View abstract, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3306530.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Moustras, Marios Zacharias. "Imine formation relating to cross-linking in cellular macromolecules." Thesis, University of Exeter, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260620.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Foster, P. A. "The computer simulation of the gas dynamics in ring galaxy formation." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375065.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Azim, Amir Affan Abdul. "Growth ring formation of selected tropical rainforest trees in Peninsular Malaysia." Master's thesis, Kyoto University, 2014. http://hdl.handle.net/2433/188776.

Full text

Abstract:

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第18338号
農博第2063号
新制||農||1023(附属図書館)
学位論文||H26||N4845(農学部図書室)
31196
京都大学大学院農学研究科森林科学専攻
(主査)教授大澤晃, 教授髙部圭司, 教授北山兼弘
学位規則第4条第1項該当

APA, Harvard, Vancouver, ISO, and other styles

21

Dad, Mohammad M. (Mohammad Mehdj). "Aminoketene. Cycloaddition of Ketenes and Imines to Yield β- or δ- Lactams." Thesis, University of North Texas, 1991. https://digital.library.unt.edu/ark:/67531/metadc332534/.

Full text

Abstract:

The purpose of this investigation was to provide a systematic study of the cycloaddition pf (N-alkyl-N-phenylamino)- methoxy-and dichloroketenes to various imines and to investigate the stereochemistry of these cycloadditions.

APA, Harvard, Vancouver, ISO, and other styles

22

Katkova, Olga. "Photochemical isomerization and stereoselective thermal cycloaddition reactions of conjugated nitrones." Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=bgsu1123003688.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Moss, Neil. "Divinylcyclopropane rearrangements : preparation of tricyclic ring systems and a formal total synthesis of (±)-quadrone." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25942.

Full text

Abstract:

The first section of this thesis describes three model studies involving the synthesis of the divinylcyclopropanes (135), (136), and (137) and the subsequent thermal rearrangement of these compounds to provide the interesting tricyclic compounds (139), (140), and (141). [Formula Omitted] The second section of this thesis describes a formal total synthesis of the antitumor sesquiterpenoid (±)-quadrone (34). The synthesis is based on the chemistry developed in the model studies and involves the thermal rearrangement of the divinylcyclopropane (304) as the key step. The resulting product, compound (305), is- subsequently elaborated into the keto aldehyde (230), and since compound (230) has previously been converted into (t)-quadrone (34) by Burke and coworkers,¹⁰¹ the isolation of (230) comprises a formal total synthesis of the sesquiterpenoid. [Formula Omitted] The third section of this thesis describes a study involving the facile vinylmethylenecyclopropane rearrangement of enolates derived from various 7-exo-vinylbicyclo[4.1.0]heptan-2-ones.
Science, Faculty of
Chemistry, Department of
Graduate

APA, Harvard, Vancouver, ISO, and other styles

24

Rayanil, Kanok-on. "Studies of the chemistry of Tröger's base, cyclopentadienones, and 2,1-benzothiazines." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/5861.

Full text

Abstract:

Thesis (Ph. D.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed Aug. 10, 2007). Vita. Includes bibliographical references.

APA, Harvard, Vancouver, ISO, and other styles

25

姚大源 and Tai-yuen Yue. "Cycloaddition reactions of 2-vinylchromones." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1992. http://hub.hku.hk/bib/B31210661.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

老永康 and Wing-hong Lo. "Novel rearrangements of dioxodibenz[b,f]azocine." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B3121437X.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Lo, Tsz-kiu Brian, and 盧子翹. "Intermolecular [4+3] cycloaddition reactions using epoxy enol silanes." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B45877749.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Ross, Robert John. "Synthesis of an ingenane A/B-ring analogue : a model study for the total synthesis of ingenol /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487266362337137.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Lo, Wing-hong. "Novel rearrangements of dioxodibenz[b, f]azocine /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18597671.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Lang, William Jonathan. "Molecular clouds in the #lambda#-orionis ring : a new CO survey." Thesis, University of Bristol, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389119.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Zahid, Abdul. "Nitrogen heterocycles by tandem cationic cyclisation-aziridinium ion formation-nucleophilic ring opening." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426848.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Cheng, Johnathan Zandrew. "Nature's approach toward ring formation and structural diversity in ergot alkaloid biosynthesis." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/65472.

Full text

Abstract:

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011.
Vita. Cataloged from PDF version of thesis.
Includes bibliographical references.
Ergot alkaloids are fungal-derived secondary metabolites well known for a diverse array of pharmacological effects both beneficial and detrimental to human health. Historically, the ergot alkaloids have been known to cause ergotism in populations that consume grain contaminated by ergot alkaloid producing fungus. However, naturally isolated and semi-synthetic derivatives of certain ergot alkaloids have also been used to treat migraines, Parkinsonism, and tumor growth. Different fungal species such as Aspergillusfumigatus, Claviceps purpurea, and Neotyphodium lolii produce ergot alkaloids that have distinct structural features yet share a common tetracyclic ergoline ring scaffold. Mechanistic details regarding the formation of the common ergoline ring are not well understood, though the genes encoding the enzymes that carry out these cyclizations are believed to be well conserved across divergent fungal species. Here we describe in vivo gene disruption experiments in Aspergillusfumigatus that allowed us to identify candidate enzymes that were directly involved with the intramolecular cyclization of the ergoline ring. Additionally, we discuss the cloning and heterologous expression of these genes to further characterize their catalytic function. Old Yellow Enzyme homologues from the ergot gene clusters of Aspergillus fumigatus and Neotyphodium loii were shown to catalyze the formation of the D ring of the ergoline skeleton. These enzymes catalyzed either reductase or isomerase type reactions to yield distinct pathway intermediates. Mutational analysis was used to engineer an Old Yellow Enzyme that displayed both reductase and isomerase activities, thereby elucidating the mechanistic basis behind this switch in enzymatic activity. These findings present a mechanistic rationale behind nature's biosynthetic strategy toward ring cyclization and the introduction of structural diversity into the ergot alkaloid class of natural products.
by Johnathan Zandrew Cheng.
Ph.D.

APA, Harvard, Vancouver, ISO, and other styles

33

Crouch, Nicholas. "The mechanism of the enzymatic ring expansion of penicillin N to deacetoxycephalosporin C." Thesis, University of Oxford, 1988. http://ora.ox.ac.uk/objects/uuid:de3e54eb-b4b5-4673-a863-3c094cc1456d.

Full text

Abstract:

The order of events in the Deacetoxycephalosporin C/Deacetylcephalosporrn C Synthetase (DAOC/DAC Synthetase) catalysed ring expansion of penicillin N to deacetoxycephalosporin C has been investigated by the use of labelled/unlabelled penicillin N mixed competitive kinetic isotope effect experiments, in which the labelled penicillin N substrates were either labelled in the pro R- and pro S-methyl groups or at C-3. In addition, to assisting in the determination of the position of the first irreversible event in this reaction, deuteration at C-3 gave rise to a bifurcation of the natural biosynthetic pathway which led to enhanced production of the shunt metabolite, (2R,3S,6R,7R)-l-aza-3- methyl-3-hydroxy-7-[(5R)-5-amino-5-carboxy-pentanamido]-8-oxo-5-thiabicyclo[4.2.0]octane-2-carboxylate. The biosynthetic precursor to the 3S-hydroxycepham shunt metabolite has been investigated and the origin of the 3S-hydroxyl oxygen atom has been determined by the use of labelling studies with ¹⁸O₂ and shown to be derived from molecular oxygen. ¹³C-labelling studies are described which indicate that the ring expansion process is stereospecific to within the limits of the detection system employed. These experiments confirm earlier investigations but, in addition to improving upon the assessment of the degree of stereospecificity, have shown that the 3S- hydroxycepham shunt metabolite is produced with the same stereospecificity as that observed for the usual biosynthetic products, DAOC and DAC. Chapter 5 describes an investigation of the anomalous C-2 deuterium exchange detected in DAOC produced by incubation of di-(²H₃-methyl)-penicillin N with DAOC/DAC synthetase. The preliminary results from this study indicate that initially exchange occurs stereospecifically with the pro R C-2 deuterium atom being replaced by a hydrogen atom. The origins of the unusual tripeptides L-α-aminoadipyl-L-serinyl-D-valine (L,L,D-ASV), α-aminoadipyl-serinyl-isodehydrovaline (ASdV) and α-aminoadipyl-cysteinyl- β-hydroxyvaline (AC-[β-OH]-V) isolated from Penicillium chrysogenum and Cephalosporium acremonium, have been examined by the use of variously ¹³C-labelled L,L,D-α-aminoadipyl-cysteinyl-valine (L,L,D-ACV) and D,L,D-α-aminoadipyl- cysteinyl-valine (D,L,D-ACV) tripeptide isotopomers. The initial results obtained from this investigation may be considered as circumstantial evidence that ASdV is formed by the action of IPNS upon L,L,D-ACV. Finally, various substrate analogues have been prepared and evaluated as substrates for the ring expansion and hydroxylation activities of the bifunctional DAOC/DAC synthetase enzyme.

APA, Harvard, Vancouver, ISO, and other styles

34

Cwynar, Valerie A. "Studies toward the synthesis of the C₁₉ quassinoid polyandrane." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1168377607.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

McCloskey, Candice Joy. "Model studies toward the total synthesis of jatrophatrione: formation of nine-membered rings via Indian derivatives." Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/30670.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

Leung, Sze-kar, and 梁詩嘉. "Novel reactions of oxabicyclic compounds and reductive aldol cyclizations of activated alkynes." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B44570156.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Liu, Lok-lok, and 廖樂樂. "Studies toward the total synthesis of (+)-cortistatin J via an intramolecular (4+3) cycloaddition." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B4659162X.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Weddell, Derek Alexander. "Synthesis, structure determination and mechanism in thiophene derivatives." Thesis, Nottingham Trent University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343542.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Rane, Digamber Sadanand. "Acyl Imidazole : A Promising Template for Asymmetric Lewis and Brønsted Acid Mediated 1,3-Dipolar Cycloadditions." Diss., North Dakota State University, 2011. https://hdl.handle.net/10365/29336.

Full text

Abstract:

Construction of chiral complex molecules continues to be a challenge for organic chemists all over the world and to address this challenge numerous methodologies have been developed. 1,3-Dipolar cycloaddition reactions is one such simple and elegant method, which can be employed towards the construction of chiral heterocycles. The ability to construct multiple stereocenters in one operation is one of the salient features of dipolar cycloaddition reaction. Asymmetric dipolar cycloaddition via chiral Lewis or Bronsted acid catalyzed processes is aided by the development of various templates, which provide points of attachment for these catalyst. Application of acyl imidazoles as multifunctional templates has been investigated for Lewis and Bronsted acid catalyzed 1,3-dipolar cycloaddition of azomethine imines and nitrones. Chapter 1. A review of 1,3-dipolar cycloaddition towards to construction of chiral nitrogen containing heterocycles is discussed in this chapter. This chapter intends to provide the reader a current state of asymmetric 1,3-dipolar cycloaddition. Chapter 2. Development of exo and enantioselective Cu(II) catalyzed azomethine imine cycloaddition to pyrazolidinone acrylates is discussed in this chapter. The key issues approached in this chapter includes impact of metal geometry on diastereoselectivity as well as effect of N-l and C-5 substitution on enantioselectivity of cycloadducts. Investigation into the scope and limitation of azomethine imines and dipolarophiles has also been discussed. Chapter 3. This chapter introduces acyl imidazoles as multifunctional template for asymmetric azomethine imine cycloaddition. Limitation of substrate scope for azomethine imine cycloaddition encountered in the previous chapter has been resolved by the use of acyl imidazoles as templates. Synthesis of complementary diastereomers of azomethine imine cycloadducts via Lewis acid and Bronsted acid catalyzed reactions has been discussed in this chapter. Chapter 4. This chapter highlights the application of acyl imidazoles as template for first Bronsted acid catalyzed exo and enantioselective nitrone cycloaddition to electron deficient olefins. Study of appropriate chiral Bronsted acid and investigation of breadth and scope of nitrones and dipolarophiles has also been discussed here. Chapter 5. This chapter address one of the most challenging aspect of synthetic organic chemistry namely the construction of chiral quaternary stereocenters. This study highlights chiral Bronsted catalyzed nitrone cycloaddition to p,|3-disubstituted-a,P-unsaturated acyl imidazole leading to the formation of isoxazolidines with chiral quaternary stereocenter. This methodology is useful for the construction of chiral fluorinated heterocycles.

APA, Harvard, Vancouver, ISO, and other styles

40

Rane, Digamber Sadanand. "Acyl Imidazole : A Promising Template for Asymmetric Lewis and Br?nsted Acid Mediated 1,3-Dipolar Cycloadditions." Diss., North Dakota State University, 2011. https://hdl.handle.net/10365/29336.

Full text

Abstract:

Construction of chiral complex molecules continues to be a challenge for organic chemists all over the world and to address this challenge numerous methodologies have been developed. 1,3-Dipolar cycloaddition reactions is one such simple and elegant method, which can be employed towards the construction of chiral heterocycles. The ability to construct multiple stereocenters in one operation is one of the salient features of dipolar cycloaddition reaction. Asymmetric dipolar cycloaddition via chiral Lewis or Bronsted acid catalyzed processes is aided by the development of various templates, which provide points of attachment for these catalyst. Application of acyl imidazoles as multifunctional templates has been investigated for Lewis and Bronsted acid catalyzed 1,3-dipolar cycloaddition of azomethine imines and nitrones. Chapter 1. A review of 1,3-dipolar cycloaddition towards to construction of chiral nitrogen containing heterocycles is discussed in this chapter. This chapter intends to provide the reader a current state of asymmetric 1,3-dipolar cycloaddition. Chapter 2. Development of exo and enantioselective Cu(II) catalyzed azomethine imine cycloaddition to pyrazolidinone acrylates is discussed in this chapter. The key issues approached in this chapter includes impact of metal geometry on diastereoselectivity as well as effect of N-l and C-5 substitution on enantioselectivity of cycloadducts. Investigation into the scope and limitation of azomethine imines and dipolarophiles has also been discussed. Chapter 3. This chapter introduces acyl imidazoles as multifunctional template for asymmetric azomethine imine cycloaddition. Limitation of substrate scope for azomethine imine cycloaddition encountered in the previous chapter has been resolved by the use of acyl imidazoles as templates. Synthesis of complementary diastereomers of azomethine imine cycloadducts via Lewis acid and Bronsted acid catalyzed reactions has been discussed in this chapter. Chapter 4. This chapter highlights the application of acyl imidazoles as template for first Bronsted acid catalyzed exo and enantioselective nitrone cycloaddition to electron deficient olefins. Study of appropriate chiral Bronsted acid and investigation of breadth and scope of nitrones and dipolarophiles has also been discussed here. Chapter 5. This chapter address one of the most challenging aspect of synthetic organic chemistry namely the construction of chiral quaternary stereocenters. This study highlights chiral Bronsted catalyzed nitrone cycloaddition to p,|3-disubstituted-a,P-unsaturated acyl imidazole leading to the formation of isoxazolidines with chiral quaternary stereocenter. This methodology is useful for the construction of chiral fluorinated heterocycles.

APA, Harvard, Vancouver, ISO, and other styles

41

Zhang, Hongkui. "1,3-dipolar cycloadditions of α, β-unsaturated sultone and sultams." HKBU Institutional Repository, 2004. https://repository.hkbu.edu.hk/etd_ra/532.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Wan, Honghe. "Allenes and (2+2+1) cycloaddition reactions." Morgantown, W. Va. : [West Virginia University Libraries], 1998. http://etd.wvu.edu/templates/showETD.cfm?recnum=195.

Full text

Abstract:

Thesis (M.S.)--West Virginia University, 1998.
Title from document title page. Document formatted into pages; contains xii, 99 p. : ill. Includes abstract. Includes bibliographical references (p. 93-99).

APA, Harvard, Vancouver, ISO, and other styles

43

Kahraman, Mehmet. "Studies of intramolecular [4+3]-cycloadditions and chiral molecular clefts /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9904851.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Diamond, Brian J. "Temperature and PH dependence of the cyclization of creatine." Huntington, WV : [Marshall University Libraries], 2005. http://www.marshall.edu/etd/descript.asp?ref=550.

Full text

APA, Harvard, Vancouver, ISO, and other styles

45

Sautermeister, Falko Alexander. "Piston ring lubrication-influence of sulphuric acid formation from high sulphur content fuel." Thesis, University of Leeds, 2012. http://etheses.whiterose.ac.uk/3132/.

Full text

Abstract:

Large 2-stroke marine diesel engines burn high sulphur content residual fuel. The sulphur converts to aqueous sulphuric acid, H2SO4, and condenses on the cylinder liner surface, where it causes corrosive attack when not neutralised by the high alkaline reserve in the lubricant. Cylinder liner wear and deposit formation are observed to reflect poor lubricant distribution, surface temperature and sulphur fuel content, which all influence acid concentration. Currently neglected by the industry, is the catalysing action of H2SO4 on lubricant degradation and the rheology of entrained droplets in the oil film, which was the motivation for this study. To understand the basic interaction of H2SO4 with the lubricant film, the Saturated hydrocarbon squalane, C30H62, was chosen as a simple model oil in addition to fully formulated lubricants and their corresponding API Group I base oils. Interfacial tension between oil and aqueous solutions of H2SO4 was measured. Contact angles of aqueous solutions of H2SO4 immersed in C30H62 on piston ring chrome coating compared to grey cast iron cylinder liner material were measured. Fully formulated lubricant and API Group I base oil was used pure and emulsified with H2SO4 to lubricate a piston ring/ cylinder contact on a Plint TE77 Tribometer. The main analytical techniques were the light microscope, SEM/EDX, XPS, FTIR, laser diffraction particle size characterisation, white-light-interferometer and viscometer. Inter facial tension measurements of aqueous H2SO4 against C30H62 reveal a close relationship with the dissociation of H2SO4, which is also reflected by the formation of bituminous emulsions with API Group I base oil when above 40% w/wH2SO4 and formation of solids when above 80% w/wH2SO4 and high temperatures of around 120–165°C or long storage times. For pure water, the contact angles were found to be large while they were small for concentrated sulphuric acid. Contact angles on chrome coating were bigger than on grey cast iron. Advancing contact angles were larger than static and receding contact angles, which was expected. During the TE77tests,the degradation temperature of the base oil was lowered when in contact with H2SO4 from 250 to 80°C for oxidation, from 300 to 170°C for nitration and from 300 to 120°C for deposit formation. Over all the appearance of the surfaces improved when sulphuric acid was added to both, the API Group I base oil and the fully formulated lubricant.

APA, Harvard, Vancouver, ISO, and other styles

46

Jones, Alan Morenc. "The synthesis of medium-sized ring containing libraries using oxidative fragmentation and rearrangement strategies /." St Andrews, 2009. http://hdl.handle.net/10023/663.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

McKibben, Bryan P. "Reactivity studies of arene-cis-diols in cycloadditions and potassium permanganate oxidations : synthesis of the corresponding arene-trans-diols and an approach to the synthesis of (+)-pancratistatin /." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-164317/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Hewitt, Russell James. "Investigations of ring-opening reactions of cyclopropanated carbohydrates : towards the synthesis of the natural product (--)-TAN-2483B : a thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry /." ResearchArchive@Victoria e-Thesis, 2010. http://hdl.handle.net/10063/1249.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

Zehr, Peter S. "Synthesis of novel alkaloids using squaric acid esters." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4411.

Full text

Abstract:

Thesis (Ph. D.)--West Virginia University, 2005.
Title from document title page. Document formatted into pages; contains xvii, 207 p. : ill. Includes abstract. Includes bibliographical references (p. 97-101).

APA, Harvard, Vancouver, ISO, and other styles

50

Yip, Kai-tai. "Oxidative palladium catalysis under aerobic condition : studies on monocyclization of [beta]-Keto amides and tandem cyclization of Alkenyl anilines /." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B34860605.

Full text

APA, Harvard, Vancouver, ISO, and other styles

We offer discounts on all premium plans for authors whose works are included in thematic literature selections. Contact us to get a unique promo code!