The observed and calculated 1 H and 13 C chemical shifts of tertiary amines and their N ‐oxides

A series of model tertiary amines were oxidized in situ in an NMR tube to amine N ‐oxides and their 1 H and 13 C NMR spectra were recorded. Next, the chemical shifts induced by oxidation (Δδ) were calculated using different GIAO methods investigating the influence of the method [Hartree‐Fock (HF), Moeller‐Plesset perturbation, density functional theory (DFT)], the functional applied in the DFT (B3LYP, BPW, OPBE, OPW91) and the basis set used [6‐31G*, 6‐311G**, 6‐311 + + G** and 6‐311 + + G(3df,3pd)]. The best results were obtained with the HF/6‐311 + + G** and OPBE/6‐311 + + G** methods. The computation/experiment comparison approach was used for the configuration prediction of chiral amine N ‐oxides—( R ) and ( S )‐agroclavine‐6‐ N ‐oxide. Copyright © 2011 John Wiley & Sons, Ltd.