Experimentally Established 15N NMR Absolute Shielding Scale for Theoretical Calculations

Ilya G Shenderovich

doi:10.1021/acs.jpca.3c02350

Experimentally Established ¹⁵N NMR Absolute Shielding Scale for Theoretical Calculations

J Phys Chem A. 2023 Jul 6;127(26):5547-5555. doi: 10.1021/acs.jpca.3c02350. Epub 2023 Jun 21.

Author

Ilya G Shenderovich¹

Affiliation

¹ Faculty of Chemistry and Pharmacy, University of Regensburg, Universitätsstr. 31, 93040 Regensburg, Germany.

PMID: 37344362
DOI: 10.1021/acs.jpca.3c02350

Abstract

The nitrogen atom of 2,6-di-tert-butyl-N,N-diethylpyridin-4-amine (DEAP) is not available for non-covalent interactions. This molecule has been used to define the reference ¹⁵N NMR absolute chemical shielding (σ^ref) required to convert between the chemical shift scale used in experiments and the absolute shielding scale used in theoretical calculations. The accuracy of the obtained σ^ref was tested for solid samples of acetanilide-¹⁵N, the protonated homodimer of pyridine-¹⁵N, and poly(4-vinylpyridine-¹⁵N). Experimental ¹⁵N NMR chemical shift tensors were compared to ¹⁵N NMR shielding tensors calculated using the TPSSh, B3LYP, and ωB97XD functionals and the polarizable continuum model approximation. General recommendations are given for the smallest reliable basis set size. The reported structure of DEAP can be used to calculate σ^ref for any other calculation method.