The General Chemistry course was studied over a six-year period (1993/94 to 1998/99). The following areas were examined: (1) In the first year of this study (1997/98), the first step was to look at the history of the General Chemistry course from it's birth in the academic years 1993/94 till 1997/98 to monitor and explore many features of the course: structure, organisation, and the changes made to the course which might affect the original pattern and objectives. The study was aimed to compare students' exam results during the time of this course (1993/94 to 1997/98) and to explore the observations made previously that exam performance was not linked to entry qualifications. (2) The research sought to identify areas of student difficulty, to find out the reasons behind these learning difficulties, and to design materials to reduce obstacles to learning. Using questionnaires and interviews along with a detailed analysis of examination scripts and overall performance of students, a detailed picture was built up of the areas of student difficulties, with some insights into the reasons for these difficulties. (3) Students' opinions about the chemistry course (both at school and university levels) were gathered in an attempt to develop an overall picture of student attitudes, especially those attitudes which might influence performance. (4) The parallel course (Chemistry-1) was also studied for comparative purposes, recognising that its aims and structures were somewhat different.

The first route looked at the alkylidenation of esters i to give -alkoxyvinylstannanes ii. A cross-coupling reaction would have given enol ester products iii, followed by an acid-induced cyclisation to give the desired benzofurans iv. (Fig. 13510A) The approach was not successful, but during the course of investigating the route, we formed the novel dimetallic reagent v, the properties of which we examined. (Fig. 13510B) We looked at a second route that involved the use of thioacetals vi. Alkylidenation of esters i was carried out followed in one case by cyclisation of the enol ethers vii formed, giving benzofuran viii (R1 = Ph). (Fig. 13510C) We also successfully carried out the second route on solid phase, where Wang and Merrifield resin-bound esters ix were alkylidenated. This was the first reported incidence of Takeda-style alkylidenations on solid phase. Cleavage of the resin-bound enol esters was achieved using mild acidic conditions. This gave ketone products x. In one case ketone x was converted into benzofuran viii (R1 = CH2CH2Ph) by deprotection followed by acid treatment. (Fig. 13510D) Finally, we carried out an alternative direct cleavage to a range of benzofurans viii, by deprotecting the resin-bound enol ether ix and then cleaving with mild acid as before. (Fig. 13510E)

The work described in this thesis is concerned with the chemistry of polymethoxylated aromatic carbonyl compounds bearing a 2,6-dioxygenated substitution pattern, with particular regard to establishing synthetic routes to biologically active chromone and chromanone systems. Syntheses of key intermediates in the approaches to the natural products stigmatellin, baicalein and LL-D253(x) (and related products) were undertaken. In chapter one the reactions of nucleophiles at the carbonyl moieties of 2,6- dioxygenated benzene carbonyl compounds are reviewed. This type of process can present special difficulties and was to prove particularly significant at various stages of the work described in subsequent chapters. Chapter two is a review of the provenance, abundance, biosynthesis, and previous syntheses of the natural products stigmatellin, baicalein and LL-D253(x), these being the targets of the synthetic work undertaken in the course of the project. Chapter three is concerned with an approach to a fragment of the stigmatellin molecule (referred to as stigmatellin fragment A) using the Vilsmeier formylation reaction, while chapter four is concerned with an alternative approach to stigmatellin fragment A using Friedel-Crafts acylation methodology. The strategies and the results obtained are described and analysed in detail. In chapter five a strategy for the synthesis of baicalein trimethyl ether is described and the results obtained are discussed.

Chapter 1 presents a review of the background and current research regarding Schiff-base olefin polymerization catalysts, with special reference to the salicylaldimine species. An attempt is made to review trends within the current literature. Chapter 2 describes the synthesis and polymerization properties of tetradentate ligands with a bibenzyl backbone at titanium and zirconium centres, prepared with the intent of sterically hindering a 1,2-Migratory Insertion into the ligand imine functionality. A custom-built polymerization reactor was used to determine the stability of the catalytic systems. Steric protection is moderately successful in enhancing the stability of these systems. Chapter 3 reports the synthesis and detailed polymerization behaviour of a series of group 4 catalysts based on salicyloxazoline ligands, which should be resistant to 1,2-Migratory Insertion. Comparisons are made between polymerization under different conditions, including using High-Throughput methodology to screen catalysts under a range of differing conditions rapidly. Such systems are extremely active for polymerization of ethene, but demonstrate limited stability at elevated temperature. Chapter 4 presents our investigations into the polymerization behaviour of salicyloxazoline catalysts containing a para-methoxy substituent on the phenoxy donor unit. This substituent significantly enhances the stability of the catalysts at elevated temperature. Chapter 5 explores the nature of the active species in polymerizations with group 4 salicyloxazoline species. Alkyl cations of such species are generated from metal alkyl species with borate activators, and also from metal chloride species with MAO. We conclude that the primary deactivation mechanism is loss of ligand to aluminium co-catalyst, and that the methoxy substituent prevents this. A computational approach (DFT) is also applied, to examine the catalytic pathways which may be available to various stereoisomers of the catalyst. Chapter 6 details the experimental procedures used during this work.

The design and construction of a low temperature stopped-flow apparatus is described. This equipment was developed to study reactions whose rates are too fast for other rapid flow methods and are not suitable for investigation by the rapid-reaction techniques which do not involve the mixing of reagents. Spectrophotometric observation is used and reactions may be monitored in both the ultraviolet and visible regions. The equipment is constructed from chemically inert materials and reactions may be studied down to ca. 220K. The low temperature stopped-flow apparatus wan used to study the formations of the 2,2'-bipyridyl, 1,10-phenanthroline and 2,2',2"-terpyridyl complexes of the manganese(II) ion in anhydrous methanol. The reactions between the manganese(II) ion and the first two ligands are too fast for flow methods at ambient temperatures but the kinetics and activation parameters were easily obtained at low temperatures. Whereas in aqueous solution the formation reactions of the divalent metal ions have activation enthalpies very similar to that of water exchange at the metal ion, the activation enthalpies of the reactions studied in this work are considerably greater than that of methanol exchange at the manganese(II) ion. It is suggested that a steric effect causes the high activation enthalpies. Possibly, either the first metal-ligand bond is hindered, or ring closure is rate determining. Evidence that the 2,2'-bipyridyl complex is formed with a rate determining ring closure is presented from consideration of the relative magnitude of the acid and mercuric ion induced dissociation rate constants. The kinetics of dissociation of the mono-(2,2'-bipyridyl)mangenese(II) and mono-(1,10-phenanthroline)manganese(II) ions in anhydrous methanol are also reported. The rate constants are smaller than the corresponding reactions in water, as is expected from the relative labilising effects of co-ordinated water and methanol molecules. In Chapter 3, the kinetics of formation of peroxynitrous acid (HOONO) and its decay to nitrate ion (reactions (1) and (2)) are described. HNO2 + H2O2 -H+> HOONO + H2O (1) HOONO -H+> NO3- + H+ (2) The reaction rates are measured at much higher acidities than previous studies. The existence of an acid catalysed pathway for the isomerisation of the peroxynitrous acid, which previous workers had postulated, is confirmed. The rate law for the formation process was found to be of the form (a, b and c are constants), d [HOONO]/dt = a[H+][HNO2][H2O2]/(b + c[H2O2]) which is consistent with a mechanism in which NO+ is formed as an intermediate. The spectrum of peroxynitrous acid was recorded for the first time using a continuous-flow mixing cell. Under the conditions used, reactions (1) and (2) are an example of a series first-order reaction. It we not possible to measure meaningful rate constants for the formation process directly because of the overlap with reaction (2). A least-squares method of analysing spectrophotometric data for a series first-order reaction A -k1> (B) -k2> C is described where the unknown parameters are k1, k2 and the extinction coefficient of the intermediate B. Care is needed, since two solutions fit the data equally well. These solutions correspond to a faster formation of a weakly absorbing intermediate, and a slower formation of a more strongly absorbing species. Methods of resolving the ambiguity are discussed.

This thesis is concerned with the development and application of scanning electrochemical microscopy (SECM) to investigate interfacial photoelectrochemical processes occurring at supported Ti02 surfaces. The new SECM approach, involving both amperometric and potentiometric electrodes, was used to monitor interfacial photoprocesses with high spatial resolution. A new in situ photoelectrochemical approach to chemical actinometry has been developed and used to determine the light flux through a quartz fibre employed in the SECM system. In this system an ultramicroelectrode (UME) probe is positioned with high precision at a known distance close to a TiOrcoated fibre and used to detect reactants or products of the ongoing photodegradation process. The microelectrochemical actinometry approach was developed using the well-known liquid phase potassium ferrioxalate actinometer. The approach involved recording the steadystate current for Pe(III) reduction at an SECM tip positioned close to the fibre. A step function in the light flux (off-on) was then applied and the resulting chronoamperometric behaviour due to the reduction of Fe(III) at the UME was recorded as a function of tip-fibre separation distance. A theoretical model has been developed to simulate experimental current-time profiles, which allowed the light flux through the quartz fibre to be quantified. An experimental approach to investigating the photoelectrochemical reduction of oxygen at UV-illuminated Ti02 surfaces, in aqueous aerated and oxygenated electrolyte solutions, in the absence and presence of hole scavengers, has been developed. In this new approach the chronoamperometric behaviour for oxygen reduction was recorded at an UME tip after stepping the light flux at a back-illuminated Ti02 film on and off The kinetics of the reduction process were interpreted through various theoretical models proposed in the literature. This experimental approach demonstrated a significant depletion of the oxygen concentration at the illuminated Ti02 surface, which provides a new insight into the photomineralisation process, showing the important role of oxygen in controlling the kinetics. Using an SECM potentiometric approach, the photomineralisation kinetics of a model organic pollutant, 4-chlorophenol (4-CP), in aerated and oxygenated aqueous solutions at supported Ti02 films, were quantitatively investigated. A potentiometric Agi AgCI UMB, positioned at a known distance above the Ti02 film, was used to monitor directly the cr production from the photomineralisation of 4-CP. A theoretical model, employing a Langmuir-Hinshelwood type kinetic equation, has been developed to interpret the kinetics of the photomineralisation process and determine the associated quantum efficiency. A direct correlation between oxygen consumption at the illuminated Ti02 surface and cr formation in the photomineralisation process has been found. SECM has also been used to monitor photoelectrochemical transfer kinetics at the Ti02/aqueous interface using a well-known electron scavenger, methyl viologen. The Ti02 film was in contact with a solution containing methyl viologen dication (MV2+) as the redox mediator and sodium acetate as the hole scavenger. The chronoamperometric behaviour for MV2+ reduction was recorded at an UME tip after stepping the light flux at the Ti02 film from off to on. The rate constants for the reduction process were obtained through a theoretical model based on zero-order kinetics. The substrate generation! tip collection mode of the SECM was also used to detect the MV.+ radical cation produced at the Ti02 surface at the UME tip.

The first part of this study involves the adaptation of a matrix-assisted laser desorption/ionisation (MALDI) ion source for a tandem double-focusingltime-offlight instrument (MAG-TOF). Ion trajectory modelling was carried out for defining the optimum ion optical configuration for a new extraction region and associated ion optics that were designed and constructed. Installation of the new ion source resulted in increased sensitivity and no loss of resolution. The second part of this study involves the analysis of fullerenes and fullerene derivatives by high-energy collision-induced dissociation (CID). The structure of fullerenes formed by coalescence under the conditions of laser desorption were shown to be that of a single fullerene closed-cage structure. The dissociation of exohedral fullerene hydride derivatives was investigated. The third part of this study investigates the high-energy collision-induced dissociation of polyglycol polymer ions generated by MALDI. Mechanisms have been proposed for the dissociation of poly(ethylene glycol) and poly(propylene glycol). High-energy CID has been shown to be particularly useful for the determination of polymer end-group structure.

This thesis describes the synthesis and characterisation of novel cyclopalladated metallomesogens from four principal N-functionalised mesogenic ligands:(i) 4-alkyloxy-N- (4' -alkyloxybiphenyl)benzylidene, (H) terephthalylidene-bis-4-N-4' -alkyloxybenzylidene, (iii) bis( 4-alkoxybenzylidene-l ,4-phenylenediamine and (iv) 3, 6 bis- (alkyloxyphenyl)pyridazine). The ligands have been studied to determine their liquid crystalline behaviour and the phase behaviour is reported for the terephthalylidene-bis-4-N-4' -alkyloxybenzylidene series and for the 3, 6 bis-(alkyloxyphenyl)pyridazine series since no comprehensive study of either system has been reported in the literature. The co-ordination chemistry of these ligands is reported. The regiospecificity of the cyclopalladation reaction for the terephthalylidene-bis-4-N-4' -alkyloxybenzylidene and 3, 6 bis(alkyloxyphenyl)pyridazine series has been established and the influence of the primary cyc1opalladationstep on secondary cyclopalladationhas been examined. The co-ligands acetylacetonate, undecane-5,7 -dione, pentandecane-7,9-dione, nonadecane- 9,1O-dione, 2,2,6,6 tetra-methyl-heptane-3,5-dione and cyclopentadienylide have been employed to enable elaboration of the geometry of the organopalladium complexes giving diversity to the structure and physical properties of these materials.

This thesis describes the synthesis and characterisation of novel cycloplatinated 2,6- diphenylpyridine complexes and an interesting platinum carbene complex formed by an unusual intermolecular C-H activation. 2,6-Diphenylpyridine, 2,6-bis(4'-alkoxyphenyl)pyridines, 4-(4-octyloxyphenyl)-2,6- diphenylpyridine and 2,4,6-tris-(4-alkoxyphenyl)-[1,3,5]triazine have all been mono- cycloplatinated to from chloride bridged dimers. These dimers have been cleaved with various ligands including trimethylphosphine, dimethylsulfoxide and carbon monoxide. The synthesis and characterisation of the cyclometalated products of 2- phenylpyridine, and subsequent oxidation to a platinum(IV) complex has been described. A novel high yield synthetic route to the di-cycloplatination of C"N"C type ligands involving a C-H activation induced by water has also been reported. The synthesis of di- cycloplatinated 2,6-diphenylpyridine, 2,6-bis( 4'-alkoxyphenyl)pyridines and 4-(4'- octyloxyphenyl)-2,6-diphenylpyridine ligands has been recorded. The lability of the dimethylsulfoxide ligand used in the di-cyclometalation reaction is demonstrated by its substitution with trimethylphosphine, carbon monoxide and the stilbazole ligand. Thermal analyses of all the ligands and cyclometalated products have been recorded. The mesogenic behaviour of four materials has been described and discussed. This report also includes a synthetic route to a platinum carbene dimer formed from a 2,6-bis(2',4'-alkoxyphenyl)pyridine ligand.

Linear polysulfides (LPs) are widely used in high performance sealants. The typical structure of the polymer is: H(SC2H40CH2OC2H4S)nH. We have completely characterised the complex components that make up commercially used LPs, by means of electrospray ionisation mass spectrometry (ESI- MS), combined with collision induced dissociation (CID). ESI has proved to be an invaluable mass spectroscopic technique in the characterisation of linear polysulfides. The individual spectra are well-resolved, enabling conclusions to be reached about the presence of variant mers (usually associated with additional oxymethylene or oxyethylene units or a monosulfide linkage, or some combination of these), and about the identity of end-groups and nature of the repeat unit. We have also been able to use ESI-MS to study the degradation reactions of LP pre-polymers. We have obtained spectra of LPs using matrix assisted laser desorption ionisation time-of-flight mass spectrometry, MALDI-TOF-MS), but these are not as informative as spectra obtained by ESI-MS. Field desorption mass spectrometry (FD-MS) has also been successful in characterising LP samples, but this technique is less generally accessible and much more time-consuming than either ESI-MS or MALDI-TOF-MS. LPs degrade thermally and photochemically by two competing degradation pathways: i) a free radical autoxidation mechanism, and ii) a hydrolysis mechanism. UV photolysis or pyrolysis of LP pre-polymers in the presence of air or oxygen resulted in the development of carbonyl groups detectable by IR and 13C NMR spectroscopy, while 2-D NMR studies and the highly characteristic field positions of the NMR resonances show the carbonyl group to be due to a formate ester. All thin film samples of cured LP, irrespective of the LP structure and curing agent, including ZL-2264 (with an extra CH2 linkage in the repeat unit), also produce this carbonyl absorption at 1725 cm-1 when exposed to UV irradiation. The formate ester arises as a result of a conventional free radical mechanism of autoxidation; attack at the C-H bond adjacent to the ether oxygen atom leads to a hydroperoxide and hence an alkoxyl radical, followed by scission to give the formate ester. The study of liquid exudates formed when TBBP- and HDDA- cured LP cast blocks are exposed to prolonged periods of heat or UV irradiation also show the development of carbonyl bands at 1724 cm-1 in their IR spectra, again indicating that degradation is occurring at least in part via a free radical mechanism. ESI-MS studies of degraded pre-polymer samples and liquid exudates show that, in parallel with the degradation route involving oxygenation of a methylene group, there is a hydrolysis mechanism involving initial cleavage of the formal group to release formaldehyde, followed by secondary reactions to give other products detected in the ESI-MS spectrum of the photolysate/pyrolysate. This mechanism is supported by the extremely slow degradation of ZL-2264, which has no formal group. The hydrolysis mechanism is the principal route for the degradation of LP pre- polymers and TBHP- and HDDA- cured LP block samples, while LPs cured using MnO2 and NaB03 degrade almost exclusively via the free radical autoxidation pathway.