Polar effect in columnar unsymmetric 1,3,4-oxa(thia)diazoles》.pdf

Tetrahedron 70 (2014) 9204e9213 Contents lists available at ScienceDirect Tetrahedron journal homepage: /locate/tet Polar effect in columnar unsymmetric 1,3,4-oxa(thia)diazoles Tarng-Shiang Hu, Kuan-Ting Lin, Chih-Chin Mu, Hsiu-Ming Kuo, Ming-Chou Chen *, Chung K. Lai * Department of Chemistry, National Central University, Chung-Li, Taiwan, ROC a r t i c l e i n f o a b s t r a c t Article history: Three new series of heterocyclic 1,3,4-oxa(thia)diazoles 1aec were prepared and their mesomorphic Received 28 August 2014 behavior studied. All compounds 1a exhibited monotropic columnar phases, which were confirmed by Received in revised form 30 September 2014 powder XRD diffractometer. Compounds 1b were not mesogenic. The formation of columnar phases was Accepted 10 October 2014 sensitive to the substituent groups attached on the phenyl moiety; those with electron-donating groups Available online 17 October 2014 (R¼H, OCH3 ) were not liquid crystals, in contrast, other derivatives with electron-withdrawing groups 2 (R¼F, NO2) formed enantiotropic columnar phases. A Ncell and Rar value equal to 4.73 and