Synthesis and Mesomorphism of Four Series of 6-Z-n-Alkyl-α-D-Galactopyranoses

Three homologous series of 6-Z-n-alkyl-α-D-galactopyranoses, where Z represents either a carboxy group (OCO), a sulphur atom (S) or an oxypropylthio group (OC 3 H 6 S) have been synthesised starting from 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose in either two or three steps. The synthesis of the fourth series of6-O-n-alkyl-α-D-galactopyranoses (Z = O) has already been reported. The length of the terminal aliphatic chains has been varied systematically and the effect on the thermotropic liquid crystal transition temperatures prepared. An enantiotropic smectic A* phase was found for all of the homologues studied. The order of efficiency of the linking group Z in favouring liquid crystal formation for the same homologues of the 6-Z-n-alkyl-α-D-galactopyranoses is S = OCO > O > OC 3 H 6 S.