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.
Bibliographical noteImportant note from the Publisher regarding the attached version of the article: "This is the peer reviewed version of the following article: Zahn, SLV, Hammerich, O, Hansen, PE, Sauer, SPA. The best density functional theory functional for the prediction of 1H and 13C chemical shifts of protonated alkylpyrroles. J Comput Chem. 2021; 42: 1248– 1262, which has been published in final form at https://doi.org/10.1002/jcc.26540. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions."
- C and H NMR
- chemical shifts