AN AB INITO STUDY OF NMR ISOTROPIC SHIELDING BOND-LENGTH DERIVATIVES IN PHOSPHORUS-COMPOUNDS

Ab initio calculations of the effect of bond length modifications on p hosphorus nuclear magnetic resonance (NMR) shieldings have been carrie d out. Moderately large basis sets have been employed in the gauge inc luding atomic orbital (GLAO) approach at the Hartree-Fock, second-orde r Moller-Plesset (MP2), and estimated infinite order many-body perturb ation theory (EMPI) approaches employing MP2(fc)/6-31 + G(d) geometrie s. The EMPI approach yields better shielding derivatives than does Har tree-Fock (HF) or MP2, and correlation is found to be important in the shielding derivatives when it is also important in the isotropic shie lding itself. The computed phosphorus shielding bond length derivative s, partial derivative sigma/partial derivative R, in the homologous se ries H2PXHn parallel those found for other nuclei. Trends for partial derivative sigma/partial derivative R for the X atom in the same serie s reproduce the behavior predicted for a universal shielding surface f or second-row atoms but not for the corresponding first-row species. ( C) 1998 Elsevier Science B.V. All rights reserved.