Structure-property relationships in D-glucitol derivatives with two geminal hydrocarbon chains. Part 1.—Thermotropic and lyotropic liquid-crystalline behaviour

Abstract

Two homologous series of N-acyl N-alkyl 1-amino-l-deoxy-D-glucitol derivatives were prepared. In the first series (2), the alkyl chain length was kept constant (n-dodecyl) and in the second series (3) the acyl chain length was kept constant (n-tetradecanoyl). A number of acid addition salts, 4 and 5, were also prepared. The thermotropic properties of the compounds in series 2 and 3 changed from enantiotropic smectic A_d(S_Ad)via monotropic S_Ad and non-mesogenic to monotropic disordered hexagonal columnar (D_hd) and finally enantiotropic D_hd. Clearly, this change in thermotropic behaviour corresponds to a change in molecular shape from rod-like to (inverted) wedge-like. The acid addition salt 4 was found to form a D_hd phase which is similar to a normal hexagonal (H_I) phase. Several of the acid addition salts 5 showed an interesting polymorphism on heating. Initially, an S_Ad phase was formed which transformed to a D_hd phase before reaching the clearing point. The formation of lyotropic mesophases was studied qualitatively (contact preparation method) for all the compounds. The expected range of lyotropic phases in compounds 2 and 3, from normal hexagonal (H_I) in the molecules with one long and one short apolar chain to inverted hexagonal (HII) for molecules with two long apolar chains, was indeed observed. Compounds 5 formed the so-called ‘myelin figures’ when heated in the presence of water.