Abstract: | By means of X-ray investigations the structure of the SE and SA-phases of the title compounds has been studied. The lattice parameters of the orthorhombic SE structure are given. The thickness of the smectic layers is nearly the same in the SE and SA phases and agrees well with the length of the molecules in their most stretched form. That suggests a similar conformation of the alkyl chains in both phases. A model of the packing in the SA phase is discussed which is based on a dense packing with antiparallel orientation of molecules with a non-symmetrical shape. |