Phase Transition of (+)-Alkyl p-[5-(2-methylbutyl)-1,3-Dioxan-2-yl -Cinnamate and the Corresponding 1,3-Oxathiane and 1,3-Dithiane Compounds

Abstract

In our search for new ferroelectric liquid crystal compounds(+)-Alkyl-p-[5-(2-methylbutyl)-1,3-dioxan-2-yl cinnamates (8), (+)-Alkyl p-[5-(2-methylbutyl)-1,3-oxathian-2-yl cinnamates(9), and (+)-Alkyl p-[5-(2-methylbutyl)-1, 3-dithian-2-yl cinnamates (11) were synthesized, their transition temperatures determined and compared with those for (+)-2-methylbutyl 4-(5-alkyl-1,3-dioxan-2-yl)cinnamates(11), (+)-2-methylbutyl-4-(5-alkyl-1,3-oxathian-2-yl)cinnamates(12), and (+)-2-methylbutyl 4-(5-alkyl-1,3- dithian-2-yl)cinnamates (13). Compounds (8), (9), (10) have the two terminal substituents of (11), (12), (13) exchanged. Though compounds (11), (12), (13) exhibited a SmA phase, compounds (8), (9), (10) did not show any liquid crystal phases. To better understand the reason for this result, decyl p-(5- pentyl-1,3-dioxan-2-yl)cinnamate(14-1), decyl p-(5-pentyl-1,3-oxathian-2-yl)cinnamate(14-2) and decyl p-(5-pentyl-1,3-dithian-2-yl)cinnamate(14-3) were synthesized. These compounds have a normal pentyl group instead of the bulky 2-methyl-butyl group of compounds (8), (9), (10). All these compounds exhibited a nematic liquid crystal phase. In compounds (8), (9), (10), the 2-methylbutyl group is attached to the heterocyclic ring directly. This causes more steric hindrance between the terminal chain and the ring which increases the molecular width of these molecules giving a structure which is less favorable for forming liquid crystal phases.

Key Words:

• 1,3-dioxane
• 1,3-oxathiane
• 1,3-dithiane
• phase transition
• liquid crystal