Probing theoretical level effect on fluorine chemical shielding calculations

Abstract

The extensive quantum‐chemical calculations are assessed for prediction of the 19F nuclear magnetic shielding constants. The methods within domain of density functional theory (DFT) and ab initio, Hartree–Fock (HF), and second‐order Møller–Plesset perturbation theory (MP2) are employed for calculation of the 19F chemical shielding constants for a series of 30 small fluorine‐containing molecules. The importance of inclusion of four factors, namely, electron correlation treatment, triple‐ξ valence shell, diffuse function, and polarization function on calculating the fluorine NMR chemical shieldings for a variety of Pople's standard basis sets at gauge invariant atomic orbital (GIAO) and continuous set of gauge transformation (CSGT) conditions are discussed by employing the linear regression analysis. The systematic investigation performed here on the influence of the method, level of theory, and basis set size on the accuracy of 19F chemical shielding demonstrates that the presence of a high level of electron correlation factor in level as well as the polarization function in basis set leads to an accurate wave function to compute the reliable fluorine chemical shielding. The results analysis illustrates that the polarization function has a significant effect on the basis sets to minimize the difference between theoretical and experimental values in several fluorine molecules. An additional comparison of the GIAO and CSGT results is used as a supplementary study to confirm the validity of the results. The basis set dependence of fluorine chemical shielding constants verifies that GIAO provides results that are often more accurate than those that are calculated with CSGT approach at the same basis set size, as expected. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part A 42A: 140‐153, 2013.