Conformation studies by nuclear magnetic resonance spectroscopy in liquid crystal solvents. An investigation of torsional angles, reorientation, and order matrices in 3-, 4-, and 5-phenylisoxazole

Abstract

The n.m.r. spectra of 3-(1), 4-(2), and 5-phenylisoxazole (3) partially oriented in the nematic phase of a liquid crystalline solvent have been studied. A twisted conformation around the bond connecting the two rings is preferred, with a twist angle of ca. 18° for compounds (1) and (3) and ca. 20° for compound (2). Reorientation of these molecules is correlated with the internal rotation, while the direction of the principal order axis, with respect to a reference axis system fixed on the phenyl ring, depends on molecular shape.