DFT/B3-LYP study of the hydrogen-bonding cooperativity: application to (2-pyridone)2, 2-pyridone–H2O, 2-pyridone–CH3OH and 2-pyridone–CH3OCH3

DFT/B3-LYP(6-31++G**) calculations are used to provide information on closed N–H⋯O H-bonded complexes, containing two hydrogen bonds. The studied model systems with two H-bonds are the 2-pyridone dimer, 2-pyridone–H2O and 2-pyridone–CH3OH. For the sake of comparison, the open, singly H-bonded complex 2-pyridone–CH3OCH3 is also examined. In the closed H-bonded complexes, an H-bond cooperativity effect has been observed, but it depends on the linearity of the hydrogen bond N–H⋯O. For the 2-pyridone dimer, which has the perfect, linear geometry, the strongest cooperativity is observed, whereas in all the other closed H-bonded systems, the cooperativity is reduced by deformation from the linear H-bond geometry. These observations are illustrated by different correlations established between the H-bond angle and other characteristic H-bond parameters.