Mesomorphic Properties of the 4, 4′-Di(n) Alkoxybenzalazines

Abstract

We have reinvestigated the mesomorphic properties of the 4, 4′-Di(n) alkoxybenzalazines, first reported by Shaw and Brown.¹ Thirteen members of the series were prepared with the number (n) of carbon atoms varying from 1 to 16. A Nematic phase was always observed except for n ≥ 13; a monotropic smectic phase was observed for n = 5, 6 and another smectic phase for n ≥ 10. The compounds were examined with a polarizing microscope and heats of transition determined using a DSC-2 calorimeter. Our results differ from those of Shaw and Brown as they did not observe the monotropic smectic phase for n = 5, 6. They also cite a smectic phase for n = 7, 8, 9, 10 whereas we observe a smectic phase only for n ≥ 10 (n = 9, was not synthesized by us). The temperature given by Shaw and Brown for the crystal-smectic transitions for n = 7, 8, 9, 10 we identify as the temperatures of crystal-crystal transitions. Of these only n = 10 has a smectic phase and the transition temperature is considerably higher than that given by Shaw and Brown.