UNSYMMETRICALLY DISUBSTITUTED MESOGENS WITH A PHENYL RING CONTAINING LATERAL BRANCH - CRYSTAL AND MOLECULAR-STRUCTURE OF SMECTOGENIC 4-NITROBENZYL LOXYBENZOYLOXY)-5-(4-N-OCTYLOXYBENZOYLOXY)BENZOATE

The synthesis of unsymmetrically disubstituted mesogens bearing a cycl ic unit within the bulky lateral branch is described. The three-ring b asic mesogenic unit of the laterally 4-nitrobenzyloxycarbonyl substitu ted molecules has been additionally provided with chlorine atoms in on e or two positions, thus influencing the stability of the smectic A ph ases. The crystal and molecular structure of the smectogenic 4-nitrobe nzyl loxybenzoyloxy)-5-(4-n-octyloxybenzoyloxy)benzoate (NCOOB) has be en determined by X-ray analysis. NCOOB crystallizes in the triclinic s pace group <P(1)over bar> with 4 molecules per unit cell and the follo wing lattice parameters: a = 13.201(2) Angstrom, b = 16.473(3) Angstro m, c = 19.746(3) Angstrom, alpha = 96.11(2)degrees, beta = 95.34(2)deg rees, gamma = 99.92(1)degrees, V = 4178.4(1) Angstrom(3). The phenylen e bis(n-octyloxybenzoate) mesogenic basic fragment of the NCOOB molecu le has a non-planar, but optimally stretched shape, with a perfect all -trans-conformation of the alkyloxy chains and the lateral benzene rin g-containing branch is oriented parallel to it. The molecules are arra nged in lamellar sheets which are characterized by a parallel molecula r alignment with an interlocking of neighbouring molecules by their bu lky branches and intercalation of the alkyl chains.