Observation of Diastereotopic Signals in 15N NMR Spectroscopy
The first example in the literature of a compound showing anisochronous 15N atoms resulting from diastereotopicity is described. Racemic 1,3-dimethyl-2-phenyloctahydro-1H-benzimidazole was prepared and studied by 1H, 13C and 15N NMR spectroscopy. If convenient conditions were used (monitored by theoretical calculations of 2JN-H spin–spin coupling constants), two 15N NMR signals were observed and corresponded to the diastereotopic atoms. GIAO/density-functional calculations of chemical shifts were not only in good agreement with the experimental values but also served as prediction tools. This study suggests that 15N NMR spectroscopy could be used to probe chirality.