An ab inito study of NMR isotropic shielding bond length derivatives in phosphorus compounds

Abstract

Ab initio calculations of the effect of bond length modifications on phosphorus nuclear magnetic resonance (NMR) shieldings have been carried out. Moderately large basis sets have been employed in the gauge including atomic orbital (GIAO) approach at the Hartree–Fock, second-order Møller–Plesset (MP2), and estimated infinite order many-body perturbation theory (EMPI) approaches employing MP2(fc)/6-31+G(d) geometries. The EMPI approach yields better shielding derivatives than does Hartree–Fock (HF) or MP2, and correlation is found to be important in the shielding derivatives when it is also important in the isotropic shielding itself. The computed phosphorus shielding bond length derivatives, ∂ σ/∂ R, in the homologous series H 2PXH n parallel those found for other nuclei. Trends for ∂ σ/∂ R for the X atom in the same series reproduce the behavior predicted for a universal shielding surface for second-row atoms but not for the corresponding first-row species.