Observation of Diastereotopic Signals in 15N NMR Spectroscopy

The first example in the literature of a compound showing anisochronous N-15 atoms resulting from diastereotopicity is described. Racemic 1,3-dimethyl-2-phenyloctahydro-1H-benzimidazole was prepared and studied by H-1, C-13 and N-15 NMR spectroscopy. If convenient conditions were used (monitored by theoretical calculations of (2)J(N-H) spin-spin coupling constants), two N-15 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 N-15 NMR spectroscopy could be used to probe chirality.