An NMR investigation of the existence of halide and carboxylate co-solute effects on the rotational barrier about the C-N bonds in urea and thiourea

Abstract

Rotational barriers of the NH2 group in thiourea and benzylurea in solution become slightly larger in the presence of anionic hydrogen-bond acceptors. The interactions between the N-H bond and different anions were investigated in acetonitrile solution using1H{14N} variable-temperature NMR. Line-shape analyses of the spectra show a weakly anion-dependent increase in ΔG‡ of rotation, with benzoate having the strongest effect and iodide the weakest. Hydrogen-bonding acidities of benzylurea and thiourea were also measured on the Abraham solute hydrogen-bond acidity scale by proton NMR. Copyright © 2010 John Wiley & Sons, Ltd.