Nitrogen-14 chemical shifts in ureas

Abstract

¹⁴ N chemical shifts have been measured in some ureas and thioureas using double-irradiation techniques whilst observing the ¹H n.m.r. spectra of the compounds. The values are compared with those obtained previously for amides, and the results indicate that the ¹⁴N chemical shift variations found in ureas and amides are governed by the degree of delocalisation of the nitrogen lone pair of electrons. The ¹⁴N chemical shift of selenourea is also recorded.