14N chemical shifts in primary and secondary amides

The 14N chemical shifts in a series of primary and secondary amides have been obtained from the proton spectra by double irradiation techniques. The 14N shifts in the primary amides are affected only slightly by changes in the substituent on the carbonyl group, but a wider range is found for secondary amides. A qualitative explanation of the observed shift changes is put forward in terms of the effect that the various substituents, have upon the nitrogen lone pair of electrons.