Four-component relativistic chemical shift calculations of halogenated organic compounds

The calculation of nuclear magnetic resonance (NMR) properties of organic compounds with heavy elements has been a computational challenge due to the importance of relativistic effects and the cost of relativistic calculations capable of capturing these effects. The heavy-atom effect on the chemical shift of light atoms also challenges the interpretation of NMR spectra of organic compounds, since relativistic effects can affect the predicted values of protons bonded to heavy atoms by as much as 20 ppm. Here, we investigate the chemical shifts of six organic compounds with/without halogen atoms using non-relativistic and state-of-the-art four-component relativistic methods, comparing the results to available experimental data. Our study confirms the importance of relativistic effects in modeling NMR properties of organic compounds involving heavy atoms and shows that these effects cannot be properly described by non-relativistic methods. We also demonstrate that relativistic four-component calculations of NMR chemical shifts now have reached a level of maturity that allows these methods to be used routinely in theoretical studies of NMR properties of large organic compounds containing heavy elements. The accuracy of these calculations is high enough to allow them to be used in assisting in the structural characterization of natural compounds. Comparison of the GGA functionals used in the four-component relativistic density functional theory calculations shows that the PBE functional seems to be well suited for such studies. Copyright © 2013 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this paper.