Département de chimie moléculaire

The prediction of NMR shielding parameters for the N atom represents a particularly difficult task for most of the Hartree-Fock (HF)-based or d. functional theory (DFT)-based methodologies. In fact, for some mol. systems, the effect of the presence of a lone pair and multiple bonds on the N atom makes the use of higher correlated methods absolutely necessary to obtain accurate results. The authors present an extensive study covering almost the entire spectrum of nitrogen shielding, from +400 to -50 ppm. The sum-over-states d. functional perturbation theory (SOS-DFPT) was used to calc. the shielding const. of 132 different N atoms. The potential of the various SOS-DFPT local approxns. was assessed through the comparison of N atoms that belong to similar mol. systems to exptl. data. This procedure allows the authors to det. the margin of error to be considered in the SOS-DFPT calcn. of the isotropic shieldings for each type of N atom. [on SciFinder(R)]