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-HOH-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-HO. 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.