The molecular and crystal structures of dibenzobarrelene and a number of its diester derivatives, and three dibenzosemibullvalenes have been determined by the use of X-ray crystallography. The objectives of the study were to investigate whether or not the di-π-methane photorearrangement could be carried out in the solid state, and how such solid state results would differ from results obtained in solution. In addition, we were interested in investigating the extent to which intermolecular steric effects would modulate or change the course of the photorearrangement in the solid state as compared to its solution pathway with the view of developing a structure-reactivity correlation for the reaction in the solid state. All the dibenzobarrelenes underwent the di-π-methane photorearrangement in the solid state to give the corresponding dibenzosemibullvalene photoproduct(s). In the symmetrical 11,12-diester derivatives of dibenzobarrelene, only one di-π-methane photoproduct could be identified for each of the reactants. The ethyl/ethyl and isopropyl/iso-propyl diester derivatives displayed polymorphism. An absolute asymmetric synthesis was performed on one of the dimorphs of the iso-propyl/iso-propyl derivative which crystallized in a chiral space group, and a quantitative enantiomeric excess yield was obtained. The molecular structures of all the compounds studied showed different degrees of conjugation of the ester carbonyl groups to the central vinyl bond. The unsymmetrical 11,12-diester derivatives yielded regioisomeric dibenzosemibullvalene photoproducts. Generally, the reactions in the solid state were found to be more regioselective than the same reactions in solution. The observed differences of the relative quantities of regioisomeric photoproducts in the solid state are interpreted on the basis of intermolecular steric effects. In appropriate systems, intermolecular steric effects may be used to predict successfully not only the major regioisomeric product of a di-π-methane photorearrangement in the solid state, but also the major enantiomeric product. One regioisomeric photoproduct is obtained for each 9,11 and 10,11-diester derivative. The photoproducts obtained from these unsymmetrical 9,11 and 10,11-diester derivatives of dibenzobarrelene show that electronic effects may be the dominant factor which governs the photochemical reaction pathway of this class of compounds in the solid state. Overall, intermolecular steric hindrance and electronic factors affect the solid state photochemical pathway of each compound to different extents. There appears to be an interplay of electronic and steric factors in determining the reaction pathway which leads to the major product in the solid state. The dominance of one factor (steric versus electronic) over the other in the determination of the most favorable photochemical pathway is dependent upon the conformations of the ester groups and their relative extents of conjugation to the central vinyl bond, and the relative intermolecular steric environments of the ester groups or substituents involved in the first step (vinyl-benzo bridging) of the photochemical reaction. / Science, Faculty of / Chemistry, Department of / Graduate

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: This thesis reports an in-depth investigation of the intermolecular interaction motifs in secondary, primary and ammonium carboxylate salts. The investigation was conducted using the Cambridge Structural Database (CSD), together with a systematic steric-specific experimental study. The tendency in the literature has been to analyse organic salt crystal structures in terms of hydrogen bonding patterns, almost ignoring cation-anion interactions. This study focuses on the cation-anion interactions in secondary, primary and ammonium carboxylate salts, which have a direct effect on the formation of specific structural motifs. The ideas of ring-stacking and ring-laddering, which arise from the tendency of cations and anions to arrange themselves so as to maximise electrostatic interactions, have been applied to ammonium carboxylate salts. An extensive survey of organic ammonium carboxylate salt structures in the CSD has been carried out. The structural motifs in ammonium carboxylates were investigated, and a set of predictive rules for the pattern of intermolecular interactions in these salts was developed. Using these results, the formation of ring-stacking or ring-laddering in primary ammonium carboxylate salts can be predicted. The results from the CSD survey are discussed in Chapter 3. An experimental study has been carried out, which complements the results obtained from the CSD survey. The experimental study formed 19 novel ammonium carboxylate salts, of which 2 formed hydrates and 2 co-crystals of salts. The experimental results confirm what was found in the CSD survey, and this is discussed in Chapter 4. This study has found that the principle of ring-stacking and ring-laddering can be applied in a general form to the crystal structures of organic ammonium carboxylate salts. The size of the cation and the anion in these salts has a significant effect on the formation of structural motifs in the solid state. Interactions between cation and anion substituents also play an important role in the formation of particular structural motifs in ammonium carboxylate salts. / AFRIKAANSE OPSOMMING: In hierdie tesis word die intermolekulêre interaksie motiewe in die sekondêre, primêre en ammonium karbosilaat soute in-diepte ondersoek. Die studie is gedoen met behulp van die Cambridge Strukturele Databasis (CSD), saam met ‟n sistematiese steriesspesifieke eksperimentele studie. Die neiging in die literatuur is om organiese sout kristal strukture in terme van waterstofbindings patrone te analiseer sonder om katioon-anioon interaksies in ag te neem. Die studie fokus juis op hierdie katioon-anioon interaksies tussen sekondêre, primêre en ammonium karbosilaat soute wat ‟n direkte effek het op die vorming van spesifieke strukturele motiewe naamlik „ring-stacking‟ en „ring-laddering‟ wat hul oorsprong kry vanaf die neiging van katione en anione om hulself op so ‟n wyse te rangskik sodat die elektrostatiese interaksies ‟n maksimum kan bereik, op die ammonium karboksilaat soute. ‟n Volledige ondersoek van ammonium karboksilaat soute in die CSD is gedoen. Die strukturele motiewe in ammonium karboksilaat is ondersoek, en ‟n stel reels wat die patrone van intermolekulêre interaksies in hierdie soute voorspelis ontwikkel. Hierdie resultate kan gebruik word om die vorming van „ring-stacking‟ en „ring-laddering‟ in primêre ammonium karbosilaat soute te voorspel. Die resultate van die CSD ondersoek word bespreek in Hoofstuk 3. ‟n Eksperimentele studie is uitgevoer en die resultate hiervan komplimenteer die resultate van die CSD ondersoek. In die eksperimentele studie is 19 nuwe ammonium karboksilaat soute gekristaliseer, waarvan 2 hidraat-soute en 2 ko-kristal-van-soute is. Die eksperimentele resultate bevestig die bevindings van die CSD ondersoek, en dit word bespreek in Hoofstuk 4. Hierdie studie het gevind dat die beginsel van „ring-stacking‟ en „ring-laddering‟ kan in „n algemene vorm in die kristal strukture van organiese ammonium karboksilaat soute toegepas word. Die grootte van die katioon en anion in hierdie soute het ‟n beduidende effek op die vorming van strukturele motiewe in die vaste toestand. Interaksie tussen die katioon en anioon substituente speel „n belangrike rol in die vorming van spesifieke motiewe in ammonium karbosilaat soute.