The Crystal Structures of Some Calabash-Curare Alkaloids and Other Organic Molecules by X-Ray Methods

The main parts of this thesis describe the determinations of the structures of derivatives of two alkaloids of the calabash-curare series, caracurine-II and macusine-A, by X-ray methods. Another two sections deal with the determination of the crystal structure of a derivative of a naturally-occurring sesquiterpenoid lactone , geigerin, and with that of a monohalogenobenzene derivative, 2-chloro-4-nitroaniline. A considerable amount of information regarding the major portion of the chemical structure of caracurine-II was available when the analysis of this structure was begun. Nothing was known of the crystal structure or of the absolute position of the atoms in the molecule. Examinations of crystals of the isomorphous dihalide derivatives, the dimethochloride and the dimethobromide, were made but owing to difficulty in ascertaining the locations of the halide ions the work on these was abandoned at an early stage. The elucidation of the structure of caracurine-II resulted from an analysis of the dimethiodide derivative. Similarly, the greater part of the chemical structure of macusine-A was known when the X-ray analysis of crystals of the iodide derivative of this alkaloid was undertaken. The iodide ion was easily located and the structure was very readily determined. In neither the analysis of caracurine-II dimethiodide nor that of macusine-A iodide was great accuracy of the molecular parameters attempted. Consequently, the results have considerable limitations imposed upon them and the finer details of the molecular dimensions are obscured. A structure and partial stereochemistry of geigerin had been proposed when crystals of bromogeigerin acetate were received from Professor Barton. The X-ray crystal analysis of this derivative of geigerin confirmed the proposed structure. Unfortunately the substitution of the bromine atom into geigerin acetate did not occur at the expected position but at a centre which was of stereochemical interest. The outcome of this was that the relative stereochemistry of the geigerin molecule at that site at which this substitution had taken place could not be inferred from the results of the analysis. The analysis was carried out to a fair degree of accuracy. Some interesting features which can be correlated with those observed in other molecules are evident in the structure. The work on this structure analysis was shared with Miss J. A. Hamilton who performed, as far as possible, alternate series of calculations. The crystal analysis of 2-chloro-4-nitroaniline was undertaken in order to determine the finer details of the molecule, the gross structure being entirely known. The results clearly establish that, in the solid state, the nitro group of the molecule is twisted out of the plane of the benzene ring by a small amount