Synthesis, 13C NMR, and UV spectroscopic study of 13C-labeled nitrile N-oxide

13 C-labeled nitrile N -oxides ( 13 CNOs) were prepared to investigate the structural characteristics of nitrile N -oxide in solution. In the 13 C NMR spectra at room temperature, 13 C signals of 13 CNOs appeared at 35–38 ppm. The chemical shift of adjacent aromatic carbon C a to 13 CNO was remarkably upfield-shifted to indicate a positive mesomery effect of CNO. The 13 C NMR signal appeared as a triplet that originated from the scalar coupling of the adjacent 14 N nucleus, while it fused into a singlet as the temperature decreased. The UV spectra of 13 CNOs also indicated the temperature-dependent dynamic character of CNO.