Ab initio studies of H2PXYH molecules (X, Y = O, S)

Ab initio molecular orbital theory is applied to the study of PO and PS bonding in the hypervalent phosphinic (H2POOH), phosphinothioic (H2POSH), and phosphinodithioic (H2PSSH) acid molecules. Intramolecular proton exchange reactions are followed using the intrinsic reaction coordinate and Self‐Consistent‐Field energy localized orbitals. The PO and PS bonds are characterized via force constants, phosphorus d orbital populations, and localized orbitals and are best described as either normal single bonds or dative bonds augmented by π back donation from the oxygen or sulfur lone pairs. The anions of these acids are also investigated, and they are found to contain only dative bonds to sulfur and oxygen.