Prediction of ³¹P-NMR Chemical Shifts Using Empirical Models with Modest Methods and Optimally Selected Basis Sets

Abstract

The performance of the ab initio and density functional theory (DFT) functional, B3LYP and PBEPBE, in conjunction with selected basis sets for the prediction of 31 P shielding constants for small phosphorous-containing molecules is assessed. The effects of applied factors are discussed. By including the electron correlation treatment, B3LYP and PBEPBE are the most accurate methods to compute the chemical shielding for a set of small phosphines that was studied. Also, additional improvements of DFT were obtained by empirical scaling of basis sets in calculation of chemical shifts. For molecules containing only phosphorous and carbon atoms with sp 3 hybridization, the PBEPBE/6-311G(d,p) level of theory has been shown to provide reliable 31 P chemical shifts.

Spectroscopic, thermal analysis and DFT computational studies of salen-type Schiff base complexes

“…In addition, a comparison was made between the theoretically calculated 13 C chemical shift constants and the experimentally measured 13 C chemical shifts. GIAO (Gauge Including Atomic Orbital) as the most widely used approach for calculating NMR shielding tensors were applied [27][28][29][30][31][32][33]. The Gaussian 09 package was employed to perform optimization of structures and all the calculations [34].…”

Layer selection effect on solid state 13C and 15N chemical shifts calculation using ONIOM approach

“…Based on preliminary experiences [18,19,[50][51][52][53][54][55][56], three factors of electron correlation (A), triple-x valance shell (B), and diffuse function (C) were selected for a high layer of 2-layer ONIOM approach. Each factor was considered at two levels, with ( þ) and ( À ) for high and low level, respectively.…”

Probing theoretical level effect on fluorine chemical shielding calculations

“…The studied molecules are small enough, so the time of computations allows examination of a significant number of combinational methods. As suggested by the benchmarks we previously performed , four effective factors of electron correlation, triple‐ξ valence shell, diffuse function, and polarization function were selected to determine the effect of different basis functions. Therefore, a variety of Pople's standard basis sets were chosen for the NMR calculations .…”

“…The primary result of any quantum‐chemical calculation of NMR parameters is the absolute magnetic shielding tensors, which have more physical significance than the chemical shifts. A number of articles have recently appeared in the literature to discuss the accuracy of modest theoretical levels in the prediction of shielding tensors of H, C, N, P, and F nuclei, because these are the greatest important nuclei in NMR experiments and are studied in various molecules .…”