Some Organic Crystals: An X-Ray Study

This thesis deals with the study of some organic crystal structures using the method of x-ray diffraction; it is divided into three parts. Part I consists of a description of some theoretical aspects of x-ray crystal analysis. The techniques described have been limited to those which have actually been used by the author. X-ray investigations are undertaken with one of two aims in view, either to obtain more accurate molecular dimensions for molecules of known crystal structure or else to determine the structure of a molecule whose crystal, or even chemical, structure is not known. Both types of approach are described in this thesis. Part II describes the determination of more accurate parameters for three sulphone molecules. 4-4'-dichloro-diphenyl sulphone has been fully refined using the method of least squares. Accurate bond lengths and angles have been found and an analysis of the anisotropic thermal vibrations is given. The positions of the hydrogen atoms have been determined and found to be in good agreement with the positions found in a neutron diffraction study of this compound by other workers. The other two molecules studied are 4-4'-dibromodiphenyl sulphone and 4-4'-diiododiphenyl sulphone; these three sulphones are isomorphous. The analyses of these two molecules are not so complete as the previous one although they have also been approached by the three -dimensional least squares method. The molecular geometry is given although the values are not as accurate as in the case of 4-4'-dichlorodiphenyl sulphone. In Part III the attempts to elucidate the crystal structures of two molecules are described. The investigations were undertaken because of the lack of conclusive chemical evidence about their molecular structures. The study of prodigiosin, a bacterial pigment, was unsuccessful and the reasons for this are discussed. The study of a derivative of an antibiotic, fumagillin, has, however, been more satisfactory. So far only one projection has been studied but the molecule has been located in this and a possible chemical structure for the compound is suggested. A complete analysis to determine the stereochemistry will require three-dimensional data. There are two appendices to this thesis, the first is composed of all the structure factor data for the compounds studied. The second appendix gives details of the programs written for the DEUCE electronic digital computer which have been used in the crystal analyses described