The best density functional theory functional for the prediction of ¹H and ¹³C chemical shifts of protonated alkylpyrroles

Abstract

The prediction of 13C chemical shifts can be challenging with density functional theory (DFT). In this study 39 different functionals and three different basis sets were tested on three neutral alkylpyrroles and their corresponding protonated species. The calculated shielding constants were compared to experimental data and results from previous calculations at the MP2. We find that the meta‐hybrid functional TPSSh with either the Pople style basis set 6‐311++G(2d,p) or the polarization consistent basis set pcSseg‐1 gives the best results for the 13C chemical shifts, whereas for the 1H chemical shifts it is the TPSSh functional with either the 6‐311++G(2d,p) or pcSseg‐2 basis set. Including an explicit solvent molecule hydrogen bonded to NH in the alkylpyrroles improves the results slightly for the 13C chemical shifts. On the other hand, for 1H chemical shifts the opposite is true. Compared to calculations at the MP2 level none of the DFT functionals can compete with MP2 for the 13C chemical shifts but for the 1H chemical shifts the investigated DFT functionals are shown to give better agreement with experiment than MP2 calculations.

The Synergy between Nuclear Magnetic Resonance and Density Functional Theory Calculations

“…Working on a set of monoprotonated alkylpyrroles, a large set of functionals and basis sets were tested [ 54 ].…”

Computational 199Hg NMR

“…[70,71,291,292] Examination of the performance of various XC functionals implied for the calculations of NMR chemical shifts and spin–spin coupling constants can be found in a number of related publications. [ 125–132 ]…”

“…[70,71,291,292] Examination of the performance of various XC functionals implied for the calculations of NMR chemical shifts and spin-spin coupling constants can be found in a number of related publications. [125][126][127][128][129][130][131][132] Incorporating relativistic effects into the DFT theory applied for the calculation of NMR properties of compounds containing heavy elements (those like mercury) has become a top priority at present. In this sense, the DFT method is likely to be the best candidate for the extension to the relativistic domain given that DFT provides a reliable description of the electron correlation effects in the calculations of NMR parameters with a very small computational computational cost similar to that of the Hartee-Fock method.…”

Nuclear Magnetic Resonance

“…Semenov and Krivdin 26 benchmarked DFT calculations of 13 C NMR chemical shifts of some natural antimalarial compounds with a new basis set, named 3z-S, and also proposed lower cost NMR computations of large strychnobaillonine molecule. 27 Sauer et al 28 reported on TPSSh as the best density functional combined with 6-311þ þ G(2d,p) basis set for predicting 1 H and 13 C chemical shifts of protonated alkylpyrroles. The impact of relativistic effect on 13 C NMR shielding in carbide-bridged complexes was studied theoretically.…”