Non‐empirical calculations of the nuclear magnetic resonance spectra of imidazole and hydrated imidazole

The magnetic shielding constants of the 1H, 13C and 15N nuclei of imidazole are calculated for the isolated and hydrated molecules. The results show that the hydrogen bonds produce not only large variations of the chemical shifts for the nitrogen nuclei and the NH proton which are directly involved in the intermolecular bonding, but also measurable shifts for the carbon nuclei. The calculated shielding constants and their variation with hydration are discussed in relation to experimental results concerning imidazole, the 5‐membered ring of the purine bases and the imidazole ring of histidine. The calculated values of the spin‐spin coupling constants confirm that it is possible to study the tautomeric equilibrium of the imidazole ring from the measurement of these coupling constants and that spin‐spin coupling constants are not very sensitive to solvent effects.