Carbon-13 nuclear magnetic resonance spectra of isomeric oxaziridines. Effects of the nitrogen lone pair on carbon-13 chemical shifts

The carbon-13 n.m.r. spectra of several oxaziridines were measured. Aliphatic and aromatic ipso carbon atoms trans to the lone pair of nitrogen in oxaziridines were shifted upfield by c. 9 ppm, and 3.4 ppm, respectively, in comparison with isomers of inverted configuration. The results suggest that the nitrogen lone pair is partially responsible for the observed upfield shifts.