Mesomorphic Transition Temperatures for the Homologous Series of 4-n-Alkyl-4′-Cyanotolanes and Other Related Compounds

Abstract

The C₁ to C₁₂ homologues of the series of 4-n-alkyl-4′-cyanotolanes have been synthesised and their transition temperatures measured. The C₆, C₇, C₉, and C₁₁ homologues porduced enantiotropic nematic phases. Virtual nematic to isotropic liquid (N-I) transition temperatures were determined for the C₁ and C₂ derivatives; all the other homologues produced monotropic mesophases. The overall shapes of the N-I transition curvesl for the odd and even homologues are unusual. Smectic properties were not observed until after the C₁₀ homologueδ. The N-I transition temperatures for the 4′-c-octyl and 4′-heptyloxy derivatives of 4-cyanostilbene were higher (∼30[ddot]C) than those of the corresponding tolane derivatives. However the stilbene derivatives were highly unstable. The isomeric compounds 4-cyano-4′-(4″-octylphenyl) tolane and 4-(4″-cyanophenyl)-4′-octyltolane were found to exhibit smectic A and nematic phases, while the bromo-substituted precurors of these compounds exhibited smectic E, B, and A phases.