Molecular mechanics studies of the steric energies of cyclic phosphates and phosphites reveal that the magnitude of the ^1^7O NMR chemical shift is not only determined by the local van der Waals interaction energy, but also influenced by the local dipole interaction energy. Furthermore, the δ-compression effect of the exocyclic oxygen plays an important role in this respect, as the result of the local van derr Waals interactions. As found by us the ^3^3S NMR chemical shift of dialkylsulfones is linearly correlated with the local van der Waals interaction energy, the regression analysis provides an excellant correlation coefficient.

Key words: MOLECULAR MECHANICS, STRUCTURAL EFFECT, CHEMICAL SHIFT, NMR, VAN DER WAALS' FORCES, OXYGEN ATOM, PHOSPHOROUS ACID ESTER