Density functional theory (DFT) and second-order Møller - Plesset perturbation theory (MP2) are applied to determine the hydrogen bonding interaction energies in pyridine - water and in a set of methyl-substituted pyridine - water complexes. The results show that methyl substitution stabilizes the hydrogen bond and the degree of stabilization varies with the number and the position of methyl groups. It is demonstrated that the MP2 method yields more reliable relative stabilities for these complexes than does the applied DFT method, which does not take proper account of the dispersion interactions between water and the methyl groups in ortho positions. The comparison of the order of the computed association energies of methyl-substituted pyridine - water complexes with the experimentally observed sequence of the ease of miscibility of these molecules with water shows that there is no simple relationship between the miscibility behavior and the strength of hydrogen bond formed between water and methyl derivatives of pyridine.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry