Crystalline-state conformational change of β-nitrostyrenes and its freezing at low temperature

Abstract

The crystal structures of three β-nitrostyrenes were examined by X-ray diffraction analysis at various temperatures. At room temperature, disordered structures were observed in all the crystals, where the molecules took two conformations with different orientations. The disorders were found to be dynamic and the populations of the minor conformers decreased as the temperature was decreased. The observed dynamic disorders were accounted for in terms of a conformational change through a pedal motion in crystals. The detailed analysis of temperature dependence of the populations revealed that the solid-state pedal motions of β-nitrostyrenes were frozen in at low temperature.