Molecular mechanics (MM3) calculations on oxygen-containing phosphorus (coordination IV) compounds

An MM3 force field has been developed for small oxygen-containing phosphoru s (coordination IV) compounds. Experimental electron and neutron diffractio n, X-ray, and infrared spectral data were utilized in parametrization when available. Results from previous ab initio calculations at both the restric ted Hartree-Fock (RHF) and second-order Moller-Plesset (MP2) levels of theo ry with the standard 6-31G** basis set supplemented missing structural data , rotational profiles, and vibrational frequencies. Negative hyperconjugati on (the anomeric effect) affects the structures and energies of the molecul es under study which contain one or more sp(3)-hybridized oxygen atoms. Nat ural bond order (NBO) analysis was helpful in identifying the key orbital i nteractions involved in this effect.