Conformation of microhydrated ethylimidazole isomers explored by microwave spectroscopy
Year: 2026
Type: article
Abstract: Chirped-pulse Fourier transform microwave spectroscopy (2.0-18.5 GHz) has been employed to determine the molecular structures of isolated N-ethylimidazole and 2-ethylimidazole and to investigate the structure and intermolecular interactions within N-ethylimidazole⋯H2O, 2-ethylimidazole⋯H2O, and N-ethylimidazole⋯(H2O)2. All species probed were isolated in the cold environment of a gas sample undergoing supersonic expansion prior to recording of their pure rotational spectra. Density functional theory calculations were performed to aid spectral assignments and provide further information. Consistent with the results of the density functional theory calculations, N-ethylimidazole was observed to adopt a C1 geometry when isolated and also when subsumed into N-ethylimidazole⋯H2O and N-ethylimidazole⋯(H2O)2. The isolated 2-ethylimidazole molecule was observed to be Cs but adopts a C1 geometry within 2-ethylimidazole⋯H2O. Re-orientation of the ethyl group within 2-ethylimidazole is governed by a shallow potential energy surface. Spectroscopic parameters that include rotational constants (A0, B0, and C0), centrifugal distortion constants (DJ, DJK, and d1), and nuclear quadrupole coupling constants of nitrogen nuclei have been determined by fitting parameters in a model Hamiltonian to observed transition frequencies. Precise values of intermolecular bond lengths and angles have been determined by fitting to experimentally determined moments of inertia for a range of isotopologues. All of the hydrates observed during the present work contain a primary hydrogen bond between O-H and the pyridinic nitrogen atom of the imidazole ring and also a weaker hydrogen bond between an O atom of H2O and the substituent group on the C2 atom of the imidazole ring.
Source: The Journal of Chemical Physics
DOI: 10.1063/5.0351003
Authors: Charlotte N. Cummings, Nicholas R. Walker
Institution: Newcastle University
Language: English
Subfield: Spectroscopy
Field: Chemistry
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,500
OpenAlex ID: W7225658031