Conformational Relative Stability and Thermal Properties of Succinonitrile in Gas and Condensed Phases: Using CCSD and DFT Calculations

Abstract

The geometry and relative stability of succinonitrile in the gas phase have been studied using DFT and ab initio calculations. The trans 1(A) and gauche 1(B) conformers found in succinonitrile are stemmed from the different positions of the two nitrile groups relative to each other. Our results suggest that the trans conformer is more stable than the gauche geometry by 0.65 and 1.01 kcal/mol using the CCSD/6‐311G+(d) and M06/ aug‐cc‐pVDZ calculations, respectively. The results from population analysis indicate that the gas phase is 64.4 % abundant of trans conformer. To imitate the crystal phase, unit cells containing four succinonitrile molecules have been optimized. The data suggest that the trans molar volume of the condensed phase 5(A, B) is smaller than the gauche form 4(A, B, C) by ∼50 Å3 per unit cell. Therefore, at extremely high pressures of up to about 2.9 GPa, the trans conformer predominates. On the contrary, the gauche conformer becomes the predominant isomer as the temperature of the system decreases. This is attributed to the higher stability exhibited by the gauche conformer unit cells compared to that of the trans conformer.