Molecular Mechanics (MM3) Calculations on Oxygen-Containing Phosphorus (Coordination IV) Compounds

An MM3 force field has been developed for small oxygen-containing phosphorus (coordination IV) compounds. Experimental electron and neutron diffraction, X-ray, and infrared spectral data were utilized in parametrization when available. Results from previous ab initio calculations at both the restricted Hartree−Fock (RHF) and second-order Møller−Plesset (MP2) levels of theory with the standard 6-31G** basis set supplemented missing structural data, rotational profiles, and vibrational frequencies. Negative hyperconjugation (the anomeric effect) affects the structures and energies of the molecules under study which contain one or more sp3-hybridized oxygen atoms. Natural bond order (NBO) analysis was helpful in identifying the key orbital interactions involved in this effect.