Hydrogen Bonds and Ionic Forms versus Polymerization of Imidazole at High Pressures SharmaBharat Bhooshan VermaAshok K. ThomasSusy MurliChitra SharmaSurinder M. 2015 Imidazole (C<sub>3</sub>H<sub>4</sub>N<sub>2</sub>) is an important biomaterial for material research and applications. Our high-pressure Raman spectroscopic investigations combined with <i>ab initio</i> calculations on crystalline imidazole suggest that C–H---X (X = N, π) and N–H---N intermolecular hydrogen bonding interactions largely influence the nature of its structural and polymeric transformations under pressure. At pressures around ∼10 GPa, the reduction in the N---N distances close to the symmetrization limit and the emergence of the spectral features of the cationic form indicate the onset of proton disorder. The pressure-induced strengthening of the “blue-shifting hydrogen bonds” C–H---X (X = N, π) in this compound is revealed by the Raman spectra and the <i>ab initio</i> calculations. No polymer phase was retrieved on release from the highest pressure of 20 GPa in this study.