Crystal Structure Analyses of Androstane Derivatives and Organo-Arsenic Compounds

The thesis is divided into three parts: the first part is a brief review of the theory and methods of X-ray crystallography and the second and third parts contain examples of the application of the heavy atom method to structural problems in organic and organo-metallic chemistry respectively. The widespread occurrence of 4,4-dimethyl substituted 3-keto-5alpha-steroids and triterpenoids in nature and the high degree of substitution in ring A of these compounds has aroused interest in the conformation of ring A. In order to obtain quantitative information about the effect of the 1-3 interaction of the axial methyl groups on the conformation of ring A, the crystal structure analyses of 3-keto-4,4-dimethyl-5alpha-androstane-17beta-iodoacetate and its 19-nor analogue have been completed and are contained in part II of this thesis. The analyses establish that, in the solid state, ring A adopts a partially flattened chair conformation in the former case and an undistorted chair conformation in the latter. Part III contains the crystal structure analyses of three compounds, viz. triphenyl arsenic dihydroxide, triphenyl arsenic hydroxychloride and triphenyl arsenic hydroxybromide. These compounds are produced by either complete or partial hydrolysis of the corresponding triphenylarsine dihalides and have been formulated as Ph3As(OH)2 , Ph3As(OH)Cl and Ph3As(OH)Br respectively. By analogy with other compounds containing penta-coordinate group VB elements, these compounds have been assumed to adopt a trigonal bipyramidal structure. The crystal structure analysis of the dihydroxide establishes that, in the solid state, the compound is, in fact, triphenylarsine oxide monohydrate. The analyses of the hydroxyhalides establish that the halogen is not bonded to the arsenic atom in either case and that the compounds are more correctly formulated as 1:1 adducts of triphenylarsine oxide and the corresponding halogen acid. The composition of the adducts is maintained by a very short 0...Halogen hydrogen bond