Crystal Structure Analyses of Clathrates and Organic 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 accounts of seven crystal structure analyses in the fields of clathrate and organic chemistry respectively. Clathrates may be defined as molecular compounds having a regular cage structure of one component (the host compound), which physically encloses the other component or components (the guest compound). The great scientific interest of clathrate compounds and the widespread occurrence of these and related inclusion compounds in nature has aroused interest in the structure of these compounds. In order to determine the structure of the host molecular framework of the cage of the clathrates formed by 4-p-hydroxyphenyl-2,2,4-trimethylchroman (Dianin's compound) and 4-p-hydroxyphenyl-2,2,4-trimethylthiachroman and in order to obtain information concerning the effect of host-guest molecular interactions on the orientation and conformation of guest molecules within the cavity of the clathrates formed by 4-p-hydroxyphenyl-2,2,4-trimethylthiachroman, the analyses presented in Part II were undertaken. The analyses establish that the host molecules of the chroman and thiachroman clathrates are linked together by a network of hydrogen bonds and van der Waals' forces to form distinct cages, the cavities of which have an approximate hourglass shape. In addition it has been possible, by X-ray methods, to define the orientation, conformation and dimensions of a guest molecule, 2,5,5-trimethylhex-3-yn-2-ol, within the cavity of the clathrate formed by 4-p-hydroxyphenyl-2,2,4-trimethylthiachroman. It is found that the staggered conformation adopted by this conformationally labile guest molecule within the cavity is imposed upon it by the van der Waals' surface of the cavity. Part III contains the crystal structure analyses of four compounds, viz., 2,7-dihydro-3,6-di-p-tolyl-1,4,5-thiadiazepine-1,1-dioxide; 2,4-dimethyl-1,5-benzodiazepinium bromide; 3,7-dibromo cycloocta-1,5-diene and dioscorine methobromide which were undertaken in order to obtain quantitative information concerning the stereochemistry and conformation of these compounds. The structure analyses of 2,7-dihydro-3,6-di-p-tolyl-1,4,5-thiadiazepine-1,1-dioxide and 2, 4-dimethyl-1,5-benzodiazepinium bromide have succeeded in showing that the seven-membered unsaturated heterocyclic rings adopt a boat and planar conformation respectively. It has been known for more than twenty years that allylic bromination of cycloocta-1,5-diene yields a dibromide derivative. Earlier chemical and spectroscopic studies of this derivative did not lead to a successful structure determination. The molecular structure of the di-bromide has now been definitely established as 3,7-dibromocycloocta-1,5-diene by X-ray analysis. This has shown that 3,7-dibromocycloocta-1,5-diene adopts a twist-tub conformation in the solid state. Although the structure of dioscorine, an alkaloid isolated from the tubers of Dioscorea hirsuta, Blume and Dioscorea hispida Dennst., found in Java and the Philippine islands respectively, has been established by synthesis, the stereochemistry of the attachment of the lactone group was not unambiguously established The X-ray analysis has succeeded in showing that the structure consists of an iso-quinuclidine residue to which an unsaturated delta-lactone is spiro linked. The results suggest that the unsaturated delta-lactone ring adopts a flattened half-boat conformation, in general agreement with the results obtained for other saturated delta-lactones