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 π 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.