Nitrogen‐15 nuclear magnetic resonance spectroscopy. Natural abundance nitrogen‐15 spectra of the cis and trans isomers of secondary alkylformamides

The 15 NMR chemical shifts were measured of a number of N ‐substituted formamides and acetamides at the natural abundance level. The ratios of the cis and trans isomers for several N ‐alkylformamides were also determined. Substituent effects on the 15 N chemical shifts of formamides are compared with those of some other nitrogen‐containing compounds. There is a consistent pattern of behavior of the one bond spin–spin coupling constants [ 1 J ( 15 NH)] wherein the trans isomers of N ‐alkylformamides are larger than those of the cis isomers.