<i>Gauche</i>–<i>trans</i> Conformational Equilibrium of Succinonitrile under High Pressure

Organic chain molecules have considerable importance because of their conformational stability, which is fundamental to their chemical stability. The phase behaviors and conformational equilibrium of simple hydrocarbons and their derivatives under extreme conditions are of interest to research because of their applications. In situ high-pressure Raman spectroscopy studies on succinonitrile up to 24 GPa at ambient temperature have been conducted to investigate its structural properties and conformational equilibria. Succinonitrile has undergone a plastic-to-crystal phase transition around 0.7 GPa. A simultaneous conversion of <i>gauche</i> to <i>trans</i> conformation has been observed. A crystal-to-crystal phase transition has subsequently occurred around 2.9 GPa. The second high-pressure phase has remained stable up to 24 GPa. These two crystal structural transitions have also been confirmed by in situ high-pressure angle-dispersive X-ray diffraction experiments. Compared with the reported low-temperature phase, the new phases under high pressure have different molecular conformations and higher densities, which can provide better understanding of the paths of conformational transitions under different extreme conditions