*3.6. DFT-Calculations*

The calculation of NMR shifts was performed in a sequence of six calculation steps implemented in SPARTAN'20 [16]: (1) for all molecules of interest, the least energy conformers were determined using the "systematic approach" of the Merck Molecular Force Field program (MMFF). Up to 500 MMFF conformers within 40 kJ/mol above the global minimum were kept; in step (2), geometries were further optimized with a Hartry-Fock calculation (HF/3-21G); up to 200 conformers with <40 kJ/mol above the global minimum the energies were kept and (3) optimized (energies) with the DFT functional ωB97X-D and the 6-31G\* basis set; (4) for up to 100 conformers within a window of 15 kJ/mol, the geometries were calculated now with the same functional and basis set; up to 50 conformers with <10 kJ/mol were kept for step (5); for the remaining conformers, energies and Boltzmann factors (300 K) were calculated with ωB97X-V/6-311+G(2df,2p) [6-311G\*]; (6) for up to 30 resulting conformers with <10 kJ/mol the NMR data were calculated with ωB97X-D/6-31G\* using the geometries from step (4). The conformer shifts were averaged with the Boltzmann factors from step five.
