Synthesis and mesomorphism of four series of 6-Z-n-alkyl-alpha-D-galactopyranoses

Three homologous series of 6-Z-n-alkyl-alpha-D-galactopyranoses, where Z re presents either a carboxy group (OCO), a sulphur atom (S) or an oxypropylth io group (OC3H6S) have been synthesised starting from 1,2:3,4-di-O-isopropy lidene-alpha-D-galactopyranose in either two or three steps. The synthesis of the fourth series of 6-O-n-alkyl-alpha-D-galactopyranoses (Z = O) has al ready been reported. The length of the terminal aliphatic chains has been v aried systematically and the effect on the thermotropic liquid crystal tran sition temperatures prepared. An enantiotropic smectic A* phase was found f or all of the homologues studied. The order of efficiency of the linking gr oup Z in favouring liquid crystal formation for the same homologues of the 6-Z-n-alkyl-alpha-D-galactopyranoses is S approximate to OCO > O > OC3H6S.