Prediction of Nitrogen and Oxygen NMR Chemical Shifts in Organic Compounds by Density Functional Theory

Abstract

Sum-over-states density functional perturbation theory (SOS-DFPT) and Hartree−Fock (HF) theory based on the “individual gauge for localized orbitals” (IGLO) scheme were used to calculate 13C, 14N/15N, and 17O NMR chemical shifts of 23 molecules. Employing the (11s7p2d/6s2p)[7s6p2d/4s2p] basis set, SOS-DFPT chemical shifts were obtained that are clearly better than HF- or UDFT-based chemical shifts, as is reflected by mean absolute deviations of 2.8 (SOS-DFPT), 7.6 (UDFT), and 5.6 ppm (HF) for 13C chemical shifts, 11.8, 22.1, and 100.5 ppm for 14N/15N chemical shifts, and 36.4, 57.2, and 45.7 ppm for 17O chemical shifts with regard to experimental values. By estimating appropriate gas phase values for 14N/15N chemical shifts from measured solvent effects, average errors of SOS-DFPT chemical shifts are reduced to 3 ppm, which is close to uncertainties in experimental values. SOS-DFPT is the method of choice for predicting reasonably accurate NMR chemical shifts at relatively low computational cost even in c...