Correlations between ab initio and experimental data for isolated 1:1 hydrogen-bonded complexes of pyridine and imidazole derivatives with water

Correlations between selected ab initio predicted and experimentally observed properties of 1:1 H-bonded complexes of a series of pyridine derivatives with water are investigated. Specifically, relationships are found between the experimentally observed properties of proton affinity, frequency shift, and dipole moments, and the ab initio calculated values of bond distance, interaction energy, frequency shift, IR absorption intensity and charge differences obtained from Mulliken population analysis. The examined correlations were then compared with data collected for pyridine- H₂O and imidazole-H₂O complexes. Similarities were found between the correlations in the theoretically determined properties and the correlations in experimentally observed parameters. It was also found that well-defined relations could be established between the calculated and observed properties for the pyridine derivatives, but these could not be reliably extended to the imidazole systems. These similarities demonstrate that the presently available ab initio calculations are useful predictors of experimental behavior of H-bonded systems but only for chemically closely related molecules.