Method and basis set dependence of the NICS indexes of aromaticity for benzene

Łukasz Gajda; Teobald Kupka; Małgorzata A Broda; Małgorzata Leszczyńska; Krzysztof Ejsmont

doi:10.1002/mrc.4690

Method and basis set dependence of the NICS indexes of aromaticity for benzene

Magn Reson Chem. 2018 Apr;56(4):265-275. doi: 10.1002/mrc.4690. Epub 2018 Jan 8.

Authors

Łukasz Gajda¹, Teobald Kupka¹, Małgorzata A Broda¹, Małgorzata Leszczyńska¹, Krzysztof Ejsmont¹

Affiliation

¹ Faculty of Chemistry, University of Opole, 48, Oleska Street, 45-052, Opole, Poland.

PMID: 29211311
DOI: 10.1002/mrc.4690

Abstract

The role of theory level in prediction of benzene magnetic indexes of aromaticity is analysed and compared with calculated nuclear magnetic shieldings of ³ He used as NMR probe. Three closely related nucleus-independent chemical shift (NICS) based indexes were calculated for benzene at SCF-HF, MP2, and DFT levels of theory and the impact of basis set on these quantities was studied. The changes of benzene NICS(0), NICS(1), and NICS(1)zz parameters calculated using SCF-HF, MP2 and several density functionals were within 1 to 3 ppm. Similar deviations between magnetic indexes of aromaticity were observed for values calculated with selected basis sets. Only very small effect of polar solvent on benzene aromaticity was predicted. The ³ He nuclear magnetic isotropic shielding (σ) and its zz-components (σ_zz ) of helium atom approaching the centre of benzene ring from above produced similar curves versus benzene-He distance to NICS parameters calculated for similarly moving Bq ghost atom. We also propose an experimental verification of NICS calculations by designing the ³ He NMR measurement for benzene saturated with helium gas or in low temperature matrices.

Keywords: DFT; NICS; NMR; aromaticity; benzene.