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Co-crystallisation with 1,2,3,5-dithiadiazolyl radicalsRobinson, Sean Wade 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2012. / Please refer to full text for abstract
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A study towards the synthesis of dithiadiazolyl functionalised calix[4]arenesApplewhite, Malcolm 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Dithiadiazolyl heterocyclic radicals form part of an ever-growing research field in the quest for organic magnets and conducting materials due to the lone electron located within the heterocyclic ring. These compounds could potentially be used as electrical current conductors and transistors which may be developed into a molecular switch or other types of molecular devices.
This thesis describes the successful synthesis of three nitrile functionalised calix[4]arenes, mono-, distal- and tetra-, as bulky scaffolds to be used as precursors in the synthesis of dithiadiazolyl functionalised calix[4]arenes. The crystal structures of these three nitriles are reported herein for the first time. Dithiadiazolyls tend to dimerise in the solid state, thus by selecting a calix[4]arene as a bulky R-group, it was hoped to inhibit dimerisation. Furthermore, synthesis of the radicals on different positions of the calix[4]arene may also inhibit dimerisation in the solid state. The typical reaction in the synthesis of dithiadiazolyls involves the reaction between a nitrile and lithium bis(trimethylsilyl)amide followed by the formation of the dithiadiazolylium chloride salt by the addition of sulfur dichloride. The salt is subsequently reduced giving the desired dithiadiazolyl. However, the addition of lithium bis(trimethylsilyl)amide to mono-nitrile calix[4]arene in the synthesis of the mono-dithiadiazolyl functionalised calix[4]arene was unsuccessful. To investigate the incompatible nature of the electrophile and nucleophile, computational and physical experiments were conducted on the mono-nitrile calix[4]arene derivative. These avenues were pursued to determine whether the unreactive nature of the nitrile in this case is due to electronic effects.
Changes in the reaction conditions (i.e. temperature, solvent and the equivalents of nucleophile) were all varied, but this proved to be unsuccessful. Computationally, through charge calculations, it was determined that the electronic properties of the nitrile were similar to that of nitrile examples known to work in the literature. Therefore, it was established that steric effects of the calix[4]arene are playing a critical role in the unreactive nature of the nitrile. There are two non-degenerate LUMO orbitals for the nitrile as one is conjugated and the other is planar (LUMO + 1) to the aromatic system. It has been established that nucleophilic attack through the lowest energy LUMO would result in a high energy transition state due to the loss of conjugation and attack through the higher energy LUMO + 1 would result in a lower energy transition state. However, this was not possible due to the steric conditions surrounding its position relative to the nitrile. The results obtained from this study were, therefore, able to confirm that the normally suitable reaction procedure seems to be limited to less sterically encumbered nitriles. / AFRIKAANSE OPSOMMING: Dithiadiazolyl heterosikliese radikale vorm deel van 'n steeds groeiende navorsingsveld in die soeke na organiese magnete en material met geleidingsvermoë as gevolg van die ongepaarde elektron wat binne in die heterosikliese ring geleë is. Hierdie verbindings kan moontlik gebruik word as elektriese stroom geleiers en transistors wat tot 'n molekulêre skakelaar of ander tipe molekulêre toestelle ontwikkel kan word.
Hierdie tesis beskryf die suksesvolle sintese van drie nitriel gefunksionaliseerde calix[4]arene, mono-, distale- en tetra-, as lywige steiers om as voorgangers in die sintese van dithiadiazolyl gefunksionaliseerde calix[4]arene gebruik te word. Die kristal strukture van hierdie drie nitriele is hier in vir die eerste keer gerapporteer. Dithiadiazolyls is geneig om te dimeriseer in die vaste toestand. Daarom is die redenasie agter die keuse van die calix[4]arene as 'n lywige R-groep, as dimeriseering te inhibeer. Sintese van die radikale op verskillende posisies van die calix[4]arene kan dimeriseering in die vaste toestand inhibeer. Die tipiese reaksie in die sintese van dithiadiazolyls behels die reaksie tussen 'n nitriel en litium bis(trimetielsiliel)amied gevolg deur die vorming van die dithiadiazolylium chloried sout deur die byvoeging van swaeldichloried. Die sout is dan gereduseer om die gewenste dithiadiazolyl te vorm. Die toevoeging van litium bis(trimethielsiliel)amied mono-nitriel calix[4]arene in die sintese van die mono-dithiadiazolyl calix[4]arene was egter onsuksesvol. Om die oënskynlik onverenigbare aard van die electrofiel en nukleofiel te ondersoek, is rekenaar-berekeninge en fisiese eksperimente uitgevoer op die mono-nitriel calix[4]arene afgeleide. Hierdie twee maniere is gevolg om te bepaal of die onreaktiewe aard van die nitriel in hierdie geval as gevolg van elektroniese effekte is.
Wysigings in die reaksie omstandighede (d.w.s. temperatuur, oplosmiddel en die ekwivalente van nukleofiel) is gemaak, maar dit was onsuksesvol. Deur middle van ladings-berekeninge, is dit bepaal dat die elektroniese eienskappe van die nitriel soortgelyk is aan dié van nitriel voorbeelde wat in die literatuur geraporteer is. Daarom is dit vasgestel dat die steriese effekte van die calix[4]arene 'n kritieke rol in die onreaktiewe aard van die nitrile speel. Daar is nie-ontaarde LUMO orbitale vir die nitriel soos 'n mens is vervoeg en die ander is planêr (LUMO + 1) na die aromatiese stelsel. Daar is vasgestel dat nukleofieliese aanval deur die laagste energie LUMO sal lei tot 'n hoë energie oorgangstoestand as gevolg van die verlies van konjugasie. Aanval deur die hoër energie LUMO + 1 sou lei tot 'n laer energie oorgangstoestand. Dit was egter nie moontlik nie, as gevolg van die steries toestande rondom die orbital se posisie met betrekking tot die nitriel. Die resultate van hierdie studie bevestig, dus, dat die gewone reaksie proses beperk is tot minder steries verhinderde nitriele.
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Crystal engineering of porosityLloyd, Gareth Owen 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Inclusion and porosity properties of the following supramolecular solid-state hosts
were investigated:
• 2,7-dimethylocta-3,5-diyne-2,7-diol
• 2-methyl-6-phenylhexa-3,5-diyn-2-ol
• Dianin’s compound
• p-tert-butyl-calix[4]arene
• 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetramethoxy-2,8,14,20-
tetrathiacalix[4]arene
• Two discrete coordination metallocycles, [Ag2IMID2](BF4)2 and
[Cu2(BITMB)2(Cl)4]
All of these compounds form well-defined crystalline host structures. Inclusion
phenomena involving encapsulation of liquids were studied using single-crystal x-ray
diffraction methods. Several guest-free host structures (α phases) were structurally
elucidated and their gas sorption properties were investigated.
Studies of the sorption properties of seemingly nonporous materials were carried
out to provide insight into this rare phenomenon. Water and iodine sorption by a
polymorph of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetramethoxy-2,8,14,20-
tetrathiacalix[4]arene shows that the conventional perception of sorption through the
solid-state requires reassessment.
Gas sorption studies were carried out using apparatus devised and presented
here. These include sorption apparatus and a device to determine single-crystal
structures under controlled gas atmospheres.
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Metal carboxylate complexes relevant to the Fischer-Tropsch synthesisPienaar, Andrew 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / In a Fischer-Tropsch refinery environment carboxylate complexes are of
interest since the carboxylic acids present in product streams lead to
formation of carboxylate salts through leaching of process equipment and
catalysts. It is widely accepted that decomposition of organic (carboxylic)
acids catalysed by metals is controlled by the decomposition of metal salts or
complexes previously formed with such an acid. The determination of physical
and structural properties of caboxylate complexes could contribute to the
explanation of the mechanism involved in the decarboxylation of carboxylic
acids.
We have successfully determined the molecular structures of copper(II) allyl
acetate, zinc(II) formiate, zinc(II) isovaleroate, yttrium(III) acetate and
lanthanum(III) propionate. It has been established that zinc has a preferred
tetrahedral coordination in carboxylate complexes compared to the octahedral
coordination of copper, lanthanum and yttrium complexes considered. The
carboxylate O-C-O angle in these complexes range between 119° and 125°
and the conformation of the carbon chains is anti in all cases except for
copper(II) allyl acetate, where a gauche conformation is adopted.
Using structural methods such as TGA, infrared spectroscopy and X-Ray
powder diffraction and combining it with existing knowledge of yttrium
carboxylates and the effective use of computational chemistry – to calculate
favourable internal parameters, using DFT calculations and B-LYP level
theory - a likely structure for yttrium(III) propionate is proposed. The use of
infrared measurements were especially valuable towards predictions of
possible structures and the postulations of Nakamoto, on the relation between
carboxylate carbonyl stretching frequencies and the nature of the carboxylate
bond, could be used to accurately identify – except for the formiate salts of
zinc(II) and yttrium(III) – the bonding mode present in the relevant
compounds. We systematically tuned the non-cyclic organic part of the mono carboxylate
ligand by lengthening and branching of the alkyl chain and determined that
thermal decomposition and heat capacity of zinc complexes are a strong
function of the ligand, while the behaviour of analogous yttrium complexes is
hardly affected.
The thermal investigation of lanthanum(III) propionate yielded a result that is
in contrast with a previous study - where only CO2 was reported as byproduct
- and we report an alternative result which indicates formation of symmetric
ketones when the compound is heated to a high enough temperature. Earlier
general assumptions about the layer-like crystal structure of lanthanum
complexes coordinated by alkyl chain carboxylate are contradicted by the
crystallographic data we collected for this compound. The crystal packing of
lanthanum(III) propionate clearly shows a layered structure which is
unexpected for a carboxylate with such a short alkyl.
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Synthesis and characterisation of hybrid graft copolymers of polydimethylsiloxane and polymethylmethacrylateKrugel, Gretha 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Hybrid graft copolymers of polydimethylsiloxane (PDMS) and polymethylmethacrylate
(PMMA) were synthesised. PDMS macromonomers were synthesised anionically from
the cyclic D3 monomer. This living polymerisation was terminated with a [3-
(methacryloxy)propyl]-dimethylchlorosilane terminating agent which resulted in the
functionalised macromonomer. These PDMS macromonomers and MMA monomer were
copolymerised to form PMMA-g-PDMS hybrid copolymers by conventional free radical
reactions. Synthesised and commercial methacryloxy-functionalised PDMS
macromonomers having a range of molar masses were copolymerised with MMA to form
graft copolymers of various chemical compositions. PDMS content in the graft
copolymers could be varied by the amount of PDMS incorporated into the copolymer as
well as by varying the length of the PDMS side chains. Size exclusion chromatography
(SEC) results confirmed low PDI’s for the PDMS macromonomers synthesised
anionically. NMR studies allowed characterisation of the synthesised PDMS
macromonomers and PMMA-g-PDMS copolymers. It also allowed the determination of
relative ratios of PMMA:PDMS in the graft copolymers. Gradient elution chromatography
(GEC) was used successfully to monitor the presence and removal of the PDMS
macromonomer from the graft copolymer products. The influence of PDMS content of
the graft copolymers on retention time was also evaluated using this technique. Two
dimensional chromatography confirmed the formation of PMMA-g-PDMS copolymer as
well as PMMA homopolymer during some of the grafting reactions. GEC in the first
dimension was coupled to SEC in the second dimension. PAS-FTIR studies allowed
chemical characterisation of the graft copolymer and confirmed surface segregation of
the PDMS. Atomic force microscopy (AFM) was also used to study the surface
segregation of PDMS and looked at the relationship between surface polarity and
increasing PDMS content. The study showed the effect of thermal treatment on the
surface morphology of the hybrid polymers. Corona treatment was used to modify the
surface structure of the graft copolymer films. Contact angle studies provided evidence
of hydrophobic loss and recovery after corona for the hybrid polymer materials
containing PDMS. This is one of the first reported examples of hydrophobicity recovery
in these types of hybrid materials after corona treatment. Slow positron beam studies
highlighted the formation of a thin silica like layer on the surface of the films after corona
similar to that observed for pure cross-linked PDMS compounds. The positron studies
enabled estimation of the thickness of the silica like layer.
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Structural analysis of transition metal complexes of imidazole-derived ligandsPotts, Storm Victoria 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Please refer to full text to view abstract.
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α-Diimine complexes of transition metals for the polymerisation of lower α-olefins / a-Diimine complexes of transition metals for the polymerisation of lower a-olefinsFullaway, Phillip V. 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / In this study several potential polymerisation catalysts were synthesised. This was
accomplished by coordinating α-diimine ligands such as N,N'-diferrocenyldiazabutadiene
(DFDAB), N,N'-dimesityldiazabutadiene (DMDAB) as well as the
bidentate amine N,N,N',N'-tetramethylethylenediamine (TMEDA), to several transition
metals.
The multi-step synthesis of N,N'-diferrocenyldiazabutadiene (DFDAB) from ferrocene
involved the use of lithiated ferrocene, iodoferrocene, N-ferrocenylphthalimide and
aminoferrocene; the latter three were characterised. This ligand was coordinated to the
transition metal ions iron(II) and zinc(II) to form Fe(DFDAB)Cl2 and Zn(DFDAB)Cl2
respectively. 1H and 13C NMR, FT-IR and mass spectrometry revealed that the expected
product had been synthesised in a useful form.
2,4,6-Trimethylaniline reacted with glyoxal to form N,N'-dimesityldiazabutadiene
(DMDAB). The DMDAB ligand was coordinated to the transition metal ions zinc(II) and
silver(I) to form Zn(DMDAB)Cl2 and Ag(DMDAB)2 respectively. Characterisation now
also include molecular and crystallographic structural determinations by means of X-ray
diffractometry.
Another N-donor complex, Cr(CO)4(TMEDA), was also prepared by coordinating
N,N,N',N'-tetramethyl ethylenediamine (TMEDA) to Cr(CO)5(THF). This was done to
give an indication of the activity of low oxidation state complexes in the catalysis of
olefin polymerisation.
The metal-α-diimine complexes mentioned above were employed in the polymerisation
of the monomers ethylene and 1-pentene probably according to a cationic mechanism.
High density, high molar mass polyethylene products with narrow polydispersities were
obtained. The chromium(TMEDA) complex produced polyethylene exhibiting ultra-high
molar mass (> 10 000 kg/mol). The polymerisation of 1-pentene, using the
Fe(DFDAB)Cl2 complex, afforded oligo-pentene with a molar mass of ~800 g/mol. After an unsuccessful attempt to prepare the (CO)5Cr=C(OZrCp2Cl)(ferrocenyl) modified
Fischer-type carbene complex, the (CO)5Cr=C(OMe)(ferrocene) complex was eventually
insolated. Elucidation of its molecular structure was accomplished by X-ray
diffractometry.
Finally, the DFDAB-ligand was coordinated to Fe2(CO)9 to generate Fe(CO)3(DFDAB)
in another attempt to investigate the role of carbonyl groups and also low oxidation state
metals in polymerisation reactions [compare to Cr(CO)4(TMEDA) unit above]. The
sensitivity of this complex towards moisture and air prevented such action.
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Composite carbon membranes for the desalination of waterChamier, Jessica 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Electrodialysis is a method of water desalination which involves the separation of TDS through an ion-exchange membrane under a potential gradient. In this study it was attempted to reverse engineer the composite carbon ion-exchange membrane used in a prototype plant and electrochemically evaluate a prototype desalination cell. The influence of applied potential on the capacitance of the various electrode surfaces and possible electrode reactions was investigated. A model was also suggested to describe the conductivity through the membrane.
The composition of composite carbon membranes were determined by compositional analysis using various analytical tools. Elemental analysis, done with PIXE and EDS, showed that the membranes contained chloride, fluoride, oxygen, carbon, and possibly hydrogen. With LC-MS and IR it was established that the membranes consisted of two polymers with no carbonyl or aromatic functional groups. After further thermal analysis the following possible compounds remained: hexafluoropropylene tetrafluoroethylene copolymer, polychlorotrifluoroethylene (PCTFE), polyoxyethylene oxide (PEO) and polyethylene glycol (PEG). This assessment is in good agreement with the contents of US patent 4,153, 661, which describes the composite membrane.
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Chemiese karakterisering van die aroma van die heuningbosspesie Cyclopia GenistoidesCronje, Christel 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Honeybush (Cyclopia spp.) is indigenous to South Africa and consists of more than 20 species of
which only a few are used to make a herbal tea with a unique aroma and sweet taste. The aroma of
unfermented and fermented honeybush tea differs considerably, indicating that changes take place in
the chemical composition of the aroma during the fermentation process. Using a sample enrichment
probe (SEP) and gas chromatography-mass spectrometry (GC-MS), the chemical composition of the
aroma of unfermented and fermented C. genistoides, was analyzed and the resulting aroma profiles
were compared. A total of 74 compounds were identified in the unfermented honeybush aroma,
comprising, inter alia, a large number of saturated and unsaturated alcohols, aldehydes and methyl
ketones that were found to be either absent, or present in lower relative concentrations, in the aroma
of fermented honeybush. Most of these compounds, including 6-methyl-5-hepten-2-one, identified
as one of the major constituents of unfermented honeybush, are probably responsible for its grassy,
hay-like aroma. In the aroma of fermented honeybush 70 compounds were identified, of which 36
were found to be terpenoids. These compounds are probably responsible for the pleasant sweet
aroma of the fermented honeybush. For instance, the major aroma constituent in the fermented
honeybush, α-terpineol, is known to have a delicately floral and sweet odour. Other terpenoids
occuring in significant quantities in the fermented honeybush, are linalool, cis and trans linalool
oxide, nerol, geraniol, 2,6-dimethyl-1,7-octadien-3,6-diol, hexahydrofarnecyl acetone and phytol.
These terpenoids are known to have sweet, sweet-woody en floral odours that probably contribute to
the overall sweet aroma of the fermented honeybush. In the aroma of the unfermented honeybush a
total of 25 terpenoids was identified, of which geranyl acetone, β-ionone, and dihydroactinidiolide
are the most significant, since they are present in higher relative concentrations compared to the
same terpenoids in the fermented honeybush. These three terpenoids have overall woody and even
slightly green odours which contribute to the typical aroma of the unfermented honeybush. The
terpenoids present in the aroma of unfermented and fermented honeybush belong to the following
compound classes:
• Terpenes
• Terpene alcohols
• Terpene aldehydes
• Ketoterpenes
• Terpene ethers
• Terpene lactones
Apart from the terpenoids present in the aroma of unfermented and fermented honeybush, the
following classes of compounds are also present:
• Aliphatic hydrocarbons (saturated)
• Aliphatic alcohols (saturated and unsaturated)
• Phenols
• Aliphatic aldehydes (saturated and unsaturated)
• Aliphatic ketones (saturated and unsaturated)
• Aliphatic carboxylic acids (saturated)
• Esters (methyl esters, ethyl and higher esters and aromatic esters)
• Furane compounds
• Lactones
The present research was done to compare the chemical composition of the aroma of unfermented
and fermented honeybush of one particular species, namely C. genistoides, to obtain an
understanding of the evolution and/or disappearance of volatile compounds during fermentation that
ultimately could help to identify compounds or compound types and their precursors responsible for
its unique sweet aroma.
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The determination of cis and trans fatty acid isomers in partially hydrogenated plant oilsMarais, Christiaan De Wet 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Trans isomers are formed during the partial hydrogenation process of cis unsaturated fatty acids. The major source of trans fatty acids in the normal person's diet is from margarines and shortenings made from these partially hydrogenated plant and marine oils. In addition to influencing lipid risk factors for cardiovascular disease, trans fatty acids have also been implicated in breast cancer, and in poor fetal development and reduced early infant growth. In reality, trans fatty acids have been consumed for centuries, since they occur naturally in beef, mutton, butter, milk and other dairy products. Though it has been shown that these naturally occurring trans fatty acids have different effects on the health of humans. With the implementation of the new labelling law in South Africa, the trans fatty acids content of food items must be displayed on the food label. Therefore, it becomes necessary to optimise the analytical methodology for the determination of trans fatty acids in foods.
Many publications have reported on the quantification of the total concentration of trans fatty acids in food samples, while less work has been done on the identification and quantification of the different cis and trans unsaturated fatty acid isomers found in foods made from partially hydrogenated oils. The objective of this study was to standardise and optimise an analytical technique to identify and quantify the different cis and trans mono-unsaturated fatty acid isomers in local margarines and bread spreads.
Seeing that fatty acids are the group of lipids most commonly analysed by GLC and the availability of highly polar capillary columns bonded with cyanoalkyl polysiloxan phases, it was decided to use GLC for the identification and quantification of the different cis and trans isomers in a selected group of margarines. It was further decided to evaluate two BPX-70 capillary columns packed with cyanoalkyl polysiloxan phases. The one a 30 m BPX-70 capillary column, normally used for routine fatty acid analyses, and the other a 120 m BPX-70 capillary column.
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