A GIAO/DFT study of 1H, 13C and 15N shieldings in amines and its relevance in conformational analysis
The 1H, 13C and 15N absolute shieldings of 13 amines were calculated at the GIAO/B3LYP/6–311++G** level. For some compounds (ethylamine, piperidine and 1-methylpiperidine) two conformations were calculated. The 13C and 15N data could be correctly correlated with experimental chemical shifts, allowing the conformation of 1-methylpiperidine to be established. The 1H NMR absolute shieldings, although less well correlated with δ values, were used to account for the anisotropy effects of the N lone pair.