Comparison of Liquid Crystal Properties of Isoelectronic 4,4′‐Disubstituted O‐, S‐, Se‐ and Te‐Aryl Benzoates

All compounds examined in the two series of isoelectronic O‐, S‐, Se‐ and Te‐4′‐pentylphenyl 4‐heptyloxy‐ and 4‐octyloxy‐benzoates \documentclass{article}\pagestyle{empty}\begin{document}$ (\bar 7 \cdot {\rm X} \cdot {\rm 5;}\,{\rm \bar 8} \cdot {\rm X} \cdot {\rm 5;}\,{\rm X = O, S, Se, Te)} $\end{document} display nematic and smectic phases. The corresponding phase transition temperatures and enthalpies are listed and discussed. The DSC‐measurements indicate that the selenol ester \documentclass{article}\pagestyle{empty}\begin{document}$ \bar 8 \cdot {\rm Se} \cdot 5 $\end{document} shows N‐S A as well as S A ‐S C second order phase transitions as has been observed with the thiol ester \documentclass{article}\pagestyle{empty}\begin{document}$ \bar 8 \cdot {\rm S} \cdot 5 $\end{document} . No liquid‐crystal behaviour was detected in the similarly substituted phenylbenzamides \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {\bar 7 \cdot {\rm NH} \cdot {\rm 5; \bar 8} \cdot {\rm NH} \cdot {\rm 5}} \right) $\end{document} , which had been synthesized for the first time.