Molecular orbital theory of the hydrogen bond. VIII. Hydrogen bonding in H2OH2CO in relaxed singlet and triplet n → π* states

Ab initio SCF CI calculations with a minimal STO-3G basis set have been performed on the hydrogen bonded dimers in which H₂O is the proton donor to H₂CO in its relaxed singlet and triplet n→π^* states. Two dimers which are easily interconverted are found in the singet n→π^* state with hydrogen bond energies of 1.82 and 1.71 kcal/mole. The equilibrium dimer in the triplet state has a hydrogen bond energy of 2.97 kcal/mole. In both states, hydrogen bond formation occurs at the carbon atom. The structures of the dimers and the nature of the intermolecular surfaces in the regions of hydrogen bond formation are examined. Electron densities and distributions are also discussed.