AN HOMOLOGOUS SERIES OF 6-O-N-ALKYL-ALPHA-D-GALACTOPYRANOSES - SYNTHESIS AND THERMOTROPIC MESOMORPHIC PROPERTIES

An homologous series of 6-O-n-alkyl-alpha-D-galactopyranoses has been prepared. The length of the terminal chains has been varied systematic ally and the effect on the liquid crystal transition temperatures stud ied. Most homologues of the series exhibit enantiotropic smectic A ph ases. X-ray analysis indicates a lamellar structure for the smectic A phase with hydrogen-bonded carbohydrate cores at the layer centre, ei ther with no interdigitation of the tilted terminal alkyl chains but w ith a high degree of chain melting, or with some degree of chain inter calation. The 6-O-n-alkyl-alpha-D-galactopyranoses possess clearing po ints at higher temperatures than those of the corresponding n-alkyl al pha-D-galactopyranosides. The introduction of a higher degree of hydro gen bonding by the replacement of the oxygen atom in the ether linkage between the chain and the carbohydrate ring by an amide linkage leads to higher transition temperatures. The dependence of the liquid cryst alline behaviour on the position of the same alkyl substituent and the nature of the sugar in the pyranose form, as well as on the anomeric configuration of the liquid crystalline carbohydrates with four hydrox y groups, is reported.