Synthesis and Some Properties of 3,4-Difluorophenyl Trans-4?-Substituted Cyclohexane-1?-Carboxylates

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Abstract
A series of 3,4-difluorophenyl trans-4′-substituted cyclohexane-1′-carboxylates, which show nematic phases, was prepared and their transition temperatures, enthalpies and entropies were measured. 3,4-Difluorophenyl and 4-fluorophenyl trans-4′-n-pentylcyclohexane-1′-carboxylates were mixed separately with a nematic mixture A consisting of trans-4-n-alkyl-1-(4′-cyanophenyl)cyclohexanes. 3,4-Difluorophenyl trans-4′-n-pentylcyclohexane-1′-carboxylate reduces the threshold voltage more, decreases the N-I transition temperature more, reduces the bulk viscosity less and decreases the birefringence more than 4-fluorophenyl trans-4′-n-pentylcyclohexane-1′-carboxylate. 3,4-Difluorophenyl, 4-fluorophenyl, 3-fluorophenyl and phenyl trans-4′-{β-(trans-4”-n-propylcyclohexyl)-1”) ethylcyclohexane-1′-carboxylates were mixed separately with a mixture B consisting of 4-n-alkoxyphenyl frara-4′-n-alkylcyclohexane-l′-carboxylates and /ram-4-n-alkyl-l-(4′-cyanophenyl)cyclohexanes. The 3,4-difluorophenyl trans-4′-(β-(tram-4″-n-propylcyclohexyl)-l”) ethylcyclohexane-l′-carboxylate increases the threshold voltage of mixture B to the least extent. The dielectric constants parallel to the optical axis (ϵ11) and perpendicular to the optical axis (ϵ⊥) for a mixture C consisting of 3,4-difluorophenyl trans-4′-substituted cyclohexane-1′-carboxylates are 10.0 and 6.3, respectively.

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