LIQUID-CRYSTALLINE DERIVATIVES OF GALACTOSE AND GALACTITOL - DEPENDENCE OF THERMOTROPIC MESOMORPHISM ON CARBOHYDRATE FORM

An almost complete homologous series of the acyclic, open-chain 6-O-n- alkyl-D-galactitols has been prepared. Most homologues in this series exhibit an enantiotropic smectic A phase. The liquid crystal transiti on temperatures of these open-chain carbohydrates are compared with th ose of the corresponding homologues in the cyclic form, i.e., with tho se of the 6-O-n-alkyl-alpha-D-galactopyranoses. In general the carbohy drates in the open-chain form exhibit higher clearing points than thos e of the analogous cyclic pyranoses. However, the melting point of the galactitols is generally significantly lower than that of the corresp onding galactopyranoses. This leads to a much wider temperature range of the smectic A phase for the carbohydrates in the pyranose form. Th e lowest clearing point was found for related galactoses in the furano se form. Alternation was found for the clearing point of the 6-O-n-alk yl-alpha-D-galactopyranoses and the 6-O-n-alkyl-D-galactitols. Powder X-ray diffraction studies indicate a non-intercalated structure for th e crystalline state and an interdigitated arrangement in the smectic A phase with a degree of chain melting for both series.