An NMR investigation of the existence ofhalide and carboxylate co-solute effects onthe rotational barrier about the C—N bonds inurea and thiourea

Rotational barriers of the NH_2 group in thiourea and benzylurea in solution become slightly larger in the presence of anionic hydrogen-bond acceptors. The interactions between the NH bond and different anions were investigated in acetonitrile solution using ^1H{^(14)N} 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.

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