Hydrogen Bonds and Ionic Forms versus Polymerization of Imidazole at High Pressures

Abstract

Imidazole (C3H4N2) is an important biomaterial for material research and applications. Our high-pressure Raman spectroscopic investigations combined with ab initio 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 ab initio calculations. No polymer phase was retrieved on release from the highest pressure of 20 GPa in this study.

High-Pressure Study of the Vibrational Properties and Chemical Reaction of N-Vinyl-2-pyrrolidinone by Raman Spectroscopy

“…As further compression will hinder molecular diffusion, the crystal structure will be damaged and translate to amorphous phases. 21 However, in our case, some new internal modes started to emerge as some initial Raman peaks broadened and even weakened gradually. Given the changes in external and internal Raman modes, a chemical reaction that changes the structure of the molecule was likely to occur at about 15.7 GPa.…”

“…When the intermolecular distance in the crystal decreases to less than a threshold value under high pressure, it is necessary to release excessive free energy through molecular redirection or rearrangement. As further compression will hinder molecular diffusion, the crystal structure will be damaged and translate to amorphous phases . However, in our case, some new internal modes started to emerge as some initial Raman peaks broadened and even weakened gradually.…”

“…In recent years, pressurization has provided an innovative and environmentally friendly approach to synthesize new materials. − The application of pressure can significantly tune intermolecular interactions, facilitate close packing, rearrange molecules, and change the properties of chemical bonding. − Therefore, monomers may undergo structural phase transitions in a smaller volume that is more favorable for polymerization. − In most polymerization reactions of high carbon-to-hydrogen ratio under high pressure, the approaching of each unsaturated bond leads to the formation of saturated bonds. − Thus, pressure-induced polymerization provides a promising alternative to synthetic chemical routes pertaining to green chemistry for no need of any initiator or solvent and less impurities in the reactions. In addition, the products of pressure-induced polymerization through new reaction pathways contain distinct structures and properties from those produced by conventional synthetic methods. − For instance, sp 3 -hybridized nanothreads have shown extraordinary strength and stiffness, which perform better than conventional sp 2 carbon-based materials and polymers …”

Imidazole in Aqueous Solution: Hydrogen Bond Interactions and Structural Reorganization with Concentration

“…The imidazole-imidazole interactions through hydrogen bond are an important feature in the stabilisation of the crystal. 77 An attempt to simulate the crystal has been carried out also with the standard GAFF2 model, but the crystal turned out to be not stable during the simulation, very likely due to the incorrect orientational distribution of the N3-H1 hydrogen bonds. As already done in Ref.…”

Effect of Electron and Proton on Hydrogen-Bonded Imidazole Chains

“…Murli's group combines the high-pressure Raman spectroscopic with ab initio calculations on crystalline IH and suggests that the CH...X (X = N, π) and NH...N intermolecular hydrogen bonds largely influence the nature of its structural and polymeric transformations under pressure. 31 The proton transfer and rotational energy barriers in two-to seven-IH-molecule chains, with and without an excess proton, are characterized 32 by density functional theory at B3LYP/6-311++G(d,p) level.…”