Molecular orbital calculations have been carried out on a sequence of HXYPOH molecules, with X and Y = H, CH3, NH2, OH, OCH3, and F. The molecular structures are predicted with the ST0-2G* basis set. For the prediction of energies of isomerization to XYPOH species, single-point 3-21G* and 6-31G* calculations were used. The molecular dissociation energies of HXYPO to HPO + XY and to XPO + HY were calculated by augmenting the latter two basis sets with MP2 and MP3 perturbation corrections.