Influence of directions of two ester linkages on crystal structures of isomeric mesogens

In order to make clear the influence of two or more polar groups on packing modes of molecules, crystal structures have been determined for isomeric m esogens with different directions of two eater linkages, C8H17O-C6H4-X-C6H4 -Y-C6H4-OC8H17, where X=COO and Y=OOC for I and X=OOC and Y=COO for II. In crystal I, molecules are arranged so that moieties conjugated from C=O to a n alkoxyl O atom via a benzene ring have an antiparallel arrangement, resul ting in an imbricated structure. Crystal II has a lamellar structure with a small tilt, in which ester linkages of adjacent molecules come close each other. The crystal structures are closely related to the phase sequences, c rystal-SmC-nematic-isotropic for I and crystal-SmC-SmA-nematic-isotropic fo r II.