High-Pressure Crystallization and Compression of Isobutyronitrile

The structural response of a high-pressure phase of isobutyronitrile up to 6.12 GPa was studied by using high-pressure single-crystal X-ray diffraction, periodic density functional theory (DFT), and CrystalExplorer calculations. This phase is isostructural with a known low-temperature phase. Compression involves distortion of packing arrangements and shortening of hydrogen bonds. However, interaction energy calculations show stabilization from enhanced hydrogen bonds is offset by increasing steric repulsion. Steric contacts cause transient incompressibility between 1.88 and 2.17 GPa, overcome by higher pressure. Volume reduction, not hydrogen bonding, primarily drives compressibility. Significant steric repulsion develops by 5.21 GPa, preceding crystallinity degradation above 6.12 GPa.