Molecular Orbital Studies of Hydrogen Bonds. III. C=O···H–O Hydrogen Bond in H2CO···H2O and H2CO···2H2O

Ab initio LCAO–MO–SCF calculation for H₂CO···H₂O is carried out with a minimal Slater basis set. The most stable conformation has an O···H distance of 1.89 Å with <C=O···H=− 64° and a stabilization energy of 3.5 kcal/mole, about a half of that for H₂O···H₂O. Nonlinear and $\pi$ hydrogen bonds, H₂CO···2H₂O and the O···H–C hydrogen bond in H₂O···HCHO, are also studied. An energy decomposition scheme is proposed and applied to H₂CO···H₂O and H₂O···H₂O. In the latter the electrostatic energy 8.0 kcal/mole, the exchange repulsion − 9.9 kcal/mole, the polarization and dispersion energy 0.3 kcal/mole, and the delocalization energy 8.2 kcal/mole are in good agreement with Coulson's estimates.