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This thesis describes the effects of the application of high pressure to single crystals of small organic compounds. A range of different structural analysis techniques have been used with the emphasis on whole molecule interactions rather than atom-atom contacts. A study of the effect of pressure on the crystal structure of salicylaldoxime showed that the size of a pseudo-macrocyclic cavity within the structure is tuneable by compression. This cavity determines the reactivity of salicylaldoxime as a ligand, when deprotonated it is known to preferentially bind Cu 2+ ions over other cations in a bis(salicylaldoximato) complex due to the compatibility between the cavity size and the ionic radius of Cu 2+. Further compression studies on a range of substituted salicylaldoximes with different ambient cavity sizes showed that the application of pressure consistently decreases the cavity size across the whole series. Variation of substituent and the pressure yields cavities which span the covalent radii of many of the 1st transition series metal dications. This should allow the selectivity of metal extraction to be tuned using pressure. Computational studies of lattice energies and conformational energies in the compression studies of L-serine and 3-aza-bicyclo(3.3.1)nonane-2,4-dione have shown that significant molecular distortions can occur during compression of a crystal structure below 10 GPa. L-serine shows different conformations between phases with an energy difference of 40 kJ mol-1, whereas the conformation of 3-aza-bicyclo(3.3.1)nonane-2,4-dione is seen to distort within the same phase. Analysis of a database of compression studies using Hirshfeld surfaces has highlighted the fact that all different types of intermolecular interaction have a lower limit for compression, at least in the pressure regime below 10 GPa. These studies, along with theoretical calculations, have suggested a lower distance limit for H…H contacts of 1.7 A. This is potentially very useful for prediction of the effects of compression as H…H contacts are almost universal across small organic crystal structures.

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The kinetic studies of some substituted phenols in their reactions with sulphuryl chloride in chlorobenzene and at 25°C showed that the clectrophile involved is molecular sulphuryl chloride (Cl⁺-SO^-₂-Cl). In the poly methyl phenol studied, the magnitude of the effect of -CH₃ groups on the reactivity of the phenol molecule in this reaction suggested that the mechanism involves heterolytic attack of molecular sulphuryl chloride on the benzenoid nucleus. The kinetic study of 3,5-dimethyl anisole was done in benzene and showed similar effects. The reaction in all the phenols and anisole was found to be bimolecular and of second order. The ether and the phenols were activated towards electrophilic attack particularly in the para position. This was supported by the analysis of the products formed in the reaction which also helped to trace the mechanism via which the electrophile substitutes a hydrogen of the benzenoid nucleus. The compounds studied were: 2.4-xylenol. 2,6-xylenol. 3.5-xylenol. 2,3,5-trimethyl phenol. 2,3,6-trimethyl phenol. 3.5-ditertiary butyl phenol. 3.5-dimethyl anisole. The kinetic study of 3,5-xylenol was studied in great detail and was extended to three solvents: benzene, chloro-benzene and o-dichlorobenzene. In all the three cases a considerable change in second order rate constant was observed and indicated that the reaction was heterolytic in nature. The increase in the rate constant was also observed with the increase in the concentration of 3,5-xylenol in the reaction mixture and was explained due to the formation of a pi-complex between xylenol or its chlorinated products (4-chloro, 3,5-xylenol and 2,4-dichloro, 3,3-xylenol) and sulphuryl chloride and its high reactivity. With the increase in xylenol concentration more pi-complex was suggested to be formed thereby affecting the rate of reaction. Kinetics of 3,5-xylenol was also compared with 2,4,6-D₃-3s5-xylenol and O-deutero-3,5-xylenol to understand the other factors affecting the mechanism and to establish the rate determining step. Different quantities of 3,5-xylenol was also reacted with sulphuryl chloride in different mixture of solvents (benzene and chlorobenzene) to illustrate the effect of polarity of the solvent and the concentration of xylenol content on the rate of reaction. The explained behaviour of the pi-complex formed between 4-chloro, 3,5-xylenol and sulphuryl chloride was justified by the increase in second order rate constant of 3,5-dimethyl anisole, when reacted in presence of 4-chloro xylenol, with sulphuryl chloride. This study was extended to pi-complexes of 2,4-dichloro, 3,5-xyleno1,4-chloro,3,5-dimethyl anisole and 3,5-ditertiary butyl phenol formed with sulphuryl chloride. The nature and structure of T -complexes was also studied by u.v. and n.m.r. spectroscopy. The reactivity of the phenols can be described in the order: 2,3,5-Me₃-phenol > 3,5-xylenol > 2,3,6-Me₃-phenol and 3,5-dimethyl anisole > 2,4-xylenol > 2,6-xylenol > 3,5-ditertiary butyl phenol.

The aim of the research reported here was to investigate in detail the fluorodechlorination of some polychloroarenes in aprotic solvents. The particular interest of this work has been directed towards: 1) The identification of minor components in the reaction products, and 2) the isolation of intermediates by competitive and consecutive reactions and the use of such sequences preoperatively. Attempts have also been made to bring about the displacement of other groups (Meo-, p-Me-C₆H₄-SO-O-) by fluoride ion in sulpholan (tetramethylene sulphone) as methods of preparing aryl fluorides. Detailed studies have been made of the reaction of potassium fluoride with hexachlorobenzene, pentachlorobenzene, fluoropentachlorobenzene, pentachlorotoluene, pentachloroanisole, pentachlorophenyl p-toluenesulphonate, fluoro-2,3,5,6-tetrachlorobenzene, 1,2,3,4-, 1,2,3,5- and 1,2,4,5-tetrachlorobenzenes, tetrachlorophthaloyl chloride, 1,3,5-trichloro-2-nitrosobenzene, 1,3-dichloro-2-nitrosobenzene and octachloronaphthalene.

The Belousov-Zhabotinsky (BZ) reaction is the preeminent oscillating chemical reaction for the study of pattern formation in reaction-diffusion systems. The dispersal of the reaction in a water-in-oil AOT microemulsion (BZ-AOT reaction) gives rise to an extended range of patterns, including dash waves, segmented spirals and, most notably, stationary Turing patterns that are thought to be significant to an understanding of the biological process of morphogenesis. To date, these patterns have only been observed in two-dimensions using optical microscopy. In this project, nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) techniques were used along with existing optical methods in order to identify redox indicators suitable for the visualisation of pattern formation in the BZ-AOT reaction using MRI. The location of the redox indicator in the microemulsion was found to be important with respect to its application as an indicator. Thus, the use of Ru(II)(bpy)3 as an MR contrast agent was ruled out as it was found to reside within the micellar interface. Manganese, however, proved to be a viable MR indicator. Oscillations were observed in the manganese-catalysed BZ-AOT reaction through changes in the NMR relaxation times of solvent water molecules. The ability of manganese to act as an MR contrast indicator has enabled pattern formation in the BZ-AOT reaction to be visualised using MRI for the first time. Further development of the technique may allow pattern formation to be visualised in three-dimensions.

The organic solid state appears in a complex number of forms. The design, synthesis and application of solid state organic materials have a big impact upon society, e.g. pharmaceuticals. Traditionally, the process of selecting active pharmaceutical ingredients (APIs) was limited to free drug or accepted salt formulations. The cocrystallisation of APIs with a former molecule significantly increases the developmental options for APIs. Many pharmaceutical solids are prepared as polycrystalline materials in order to deliver favourable physical properties, i.e. solubility, bioavailability and stability. In such cases, the development and application of structure solution techniques via powder X-ray diffraction (pxrd) has played an ever increasing pivotal role. In this thesis a number of new multi-component materials; oxamic acid:nicotinamide, oxamic acid:isonicotinamide, fumaric acid:nicotinamide, maleic acid:nicotinamide and maleic acid:isonicotinamide, will be synthesised, via a number of synthetic methods, and fully structurally characterised. A direct comparison of structures solved by powder and single crystal diffraction, have been made in order to evaluate the reliability of structure solution from pxrd in these types of materials. The thermal behaviour of molecular materials will be presented as significant structural information can be extracted from the anisotropic expansion of molecular materials. In conjunction with the research into new multi-component materials, the structure solution of oxamic acid via pxrd, single X-ray diffraction and neutron diffraction will be investigated. Small organic molecular materials like oxamic acid provide a challenge to the crystallographer due to the similarities in the electron density surrounding each functional group in the molecule.

Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for urazole, 4-methylurazole and their deuterated derivatives. DFT calculations, at the B3-LYP/cc-pVDZ level, established that the structures and vibrational spectra of the molecules can be interpreted using a model with hydrogen-bonded water molecules, in conjunction with the conductor-like polarizable continuum solvation method. The vibrational spectra were computed at the optimised molecular geometry, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments. Solid-state pseudopotential-plane-wave DFT calculations, using the PW91 functional, were also carried out reflecting the importance of intermolecular hydrogen bonding in the solid state. Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for the anions of urazole and 4-methylurazole, and their N-deuterated derivatives. DFT calculations, at the B3-LYP/cc-pVTZ level, established that the structures and vibrational spectra of both anions can be interpreted using a model that incorporates hydrogen-bonded water molecules, in conjunction with the polarizable continuum solvation method. In the case of the urazole anion it is shown that deprotonation occurs primarily at N1 rather than N4, but there is also evidence for the second tautomeric structure in both in the solid state and in aqueous solution. The vibrational spectra were computed at the optimised molecular geometry in each case, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments. IR and Raman spectra have been obtained for N, N'–dicyclohexylcarbodiimide (DCC) in the solid state and in CHCl3 solution. Structures and vibrational spectra of isolated gas phase DCC molecules with C2 and Ci symmetries, computed at the B3-LYP/cc-pVTZ level, show that the IR and Raman spectra provide convincing evidence for a C2 structure in both the solid and CHCl3 solution states. Using a scaled quantum-chemical force field these DFT calculations have provided detailed assignments of the observed IR and Raman bands in terms of potential energy distributions. Comparison of solid state and solution spectra, together with a Raman study of the melting behaviour of DCC, revealed that no solid state effects were evident in the spectra. Homopolymeric poly(N-isopropylacrylamide) and poly(4-vinylpyridine) as well as copolymer poly(N-isopropylacrylamide/4-vinylpyridine) [poly(NIPAM/4-VP)] microgels (the latter synthesized using percentage composition of 4-VP in the range of 7.5 – 90 %, w/w in the original reaction mixture) were prepared by surfactant-free emulsion polymerization. Freeze-dried samples of the microgels were subjected to analysis by Raman spectroscopy using 632.8 nm exciting radiation from a helium-neon laser. The Raman spectral profiles of the different microgels are compared and contrasted in the 600-1100 cm-1 wavenumber region. In the case of the poly(NIPAM/4-VP) copolymer microgels, differing in monomer composition, Raman spectroscopy can be employed as a quick/easy method to ensure that co-polymerization has occurred and also to determine, semi-quantitatively, the percentage incorporation of the 4-VP monomer.

This investigation builds on a previous survey of the solid-state behaviour of pyridinedicarboxylate diesters, an overview of which is presented in Chapter 1. These compounds have been shown to form tape-like assemblies, mediated by a novel triple hydrogen bond motif. Chapter 2 examines the behaviour of a small subset of these compounds in solution, some of which appear to form tape-like aggregates, as studied by 1H NMR spectroscopy. Variable temperature Raman spectroscopy has been used to observe the disruption of the crystal architecture as the sample is heated past its melting point, and the increased strength of the tapes formed by the 2,6-diesters compared to those of the 3,5-analogues has been quantitatively demonstrated by DSC. The results of X-ray diffraction studies on the single crystals of a number of diesters formed with naphthalene and anthracene side-arms are described in Chapter 3. This series of compounds has allowed the effect of changing both the length of the alkyl linker and its position of attachment to the polyaromatic to be considered. The solid-state behaviour of a number of chlorinated and methylated diesters are compared in Chapter 4. Chapter 5 examines the crystal architecture of a number of asymmetrical monoesters and the behaviour of these systems is compared to that of the analogous diesters. Chapter 6 details the progress made towards the use of the 2,6-pyridinedicarboxylate synthon in the synthesis of functional materials. The solid-state behaviour of a number of other pyridine derivatives prepared during the course of the present study is described in Chapter 7.

The dependence of crystal structure assembly on molecular changes has been studied for mono-substituted acylanilides. A library of 255 crystal structures has been investigated. 217 structures were determined during this project and 38 originated from the CSD. A subset of 64 mono-substituted acetanilides was studied in detail for crystal structure similarities using the XPac algorithm and conformational preferences were assessed. Chapter 4 presents the crystal structures and their structural similarities, whilst Chapter 5 focuses on the theoretical conformational analysis. Three amide-amide hydrogen bond geometries and a molecular stack were frequently observed in the acetanilides. The assembly of these one-dimensional packing features governs in particular the crystal structures of the para substituted acetanilides. The amide-amide hydrogen bonded chains were very persistent in all the acylanilides. The amide substituent had a larger effect on the chain geometry than the phenyl substituent. In the crystal the molecular structures deviate from the expected planar conformation. Rotation about the amide to phenyl bond of up to 55 degrees in ortho-tertbutyl acetanilide is observed. Para-substituents affect the rotational barriers; whilst such correlation was not discernible for meta-substituents. Ortho substitution frequently produces intramolecular hydrogen bonding outweighing any other substituent effects. Although the experimental conformations deviate from the planar geometry they are still within the minimum energy well and energy penalties are small. These can be easily compensated for by intermolecular interactions in the crystal