17O NMR Spectra of Acylated Ureas and Thioureas

Abstract

17O NMR spectra of ten acyl- and diacylureas (I-V) and thioureas (VII-X) were measured. 17O NMR chemical shifts of the ureido oxygen in the ureas range from 240 to 310 ppm, those of the acyl oxygens from 377 to 400 ppm (acetyl groups) and 359 to 389 ppm (benzoyl groups), the half-widths being tens to hundreds Hz. Acylation of urea to the diacyl stage has an almost twice as large effect on the chemical shift of the ureido oxygen than has the monoacylation. From the viewpoint of 17O NMR shifts, no significant differences has been found in the influence of ureido and thioureido groups on the transfer of electronic effects in 1,3-diacylureas and 1,3-diacylthioureas.