A Study of Some Organic Crystal Structures

The crystal structure determination, using single crystal X-ray diffraction methods, of three polycyclic aromatic hydrocarbons is described. The thesis is divided into three parts, each part corresponding to one compound. An appendix is added in which the history and. uses of ''generalized projections" is reviewed. An adaption of this technique was used extensively in the analysis of 1:9-5:10 diperinaphthylene anthracene. Part I of this thesis deals with the structure of 2:3-8:9 dibenzperylene. The short b axis of the monoclinic unit cell, and the regular nature of the rings in this aromatic compound, made the structure analysis easy. The good resolution of the atoms in the projection on the (010) plane made it possible for refinement, by means of two dimensional fourier series, to proceed to a good degree of accuracy. It was, therefore, surprising that refinement by successive difference maps did not yield the same answer as a back shift correction calculated from a comparison of electron density maps for which Fobs and Fcalc values had been used as coefficients in the Fourier series. However, both methods of refinement show clearly an intermolecular approach distance of less than 3.2 A. Bond lengths appear to indicate that this is apparently due to a lack of complete planarity of the molecule, although another explanation is possible. The overcrowded aromatic hydrocarbon 1:9-5:10 diperi-naphthylene anthracene is described in Part II. The work concerns itself mainly In the solution of the phase problem, for which a number of unusual methods had to be employed. Two co-ordinates of the atoms in the molecule were found by projections on the (010) plane and the third by means of generalized projections of the (hll) planes. No great accuracy could be achieved, but it was possible to distinguish which of the two possible methods the molecule adopted to relieve the overcrowding. In the third part of the thesis a description is given of the analysis and refinement of anthrovalene, the third member of the coronene, ovalene series. This analysis is of very great interest because of the extraordinary nature of the chemical reaction in which anthrovalene was formed. It is possible that this process may give an understanding of graphitization. When the work was started not even the empirical formula was known. The cell dimensions showed clearly that the unknown compound was loosely ("isomorphous") with coronene and ovalene. The molecular weight determination left little doubt about this, and a study of the intensities gave a final confirmation. Certain impurities were, however, found in the available crystals