The confirmation of trisubstituted ureas and thioureas in solution

Abstract

Dipole moments of 1,1-dimethyl-3-arylureas Ia-Ie, measured in benzene and dioxan solutions, were interpreted in terms of the Z-conformation (A), taking into account a proper correction for the conjugation within the functional group. The conformation was corroborated on the basis of infrared spectra in several solvents, in particular referring to the amide-II band. No indication of any minor conformer was obtained. The same techniques applied to 1,1-dimethyl-3-arylthioureas IIa. IIb confirmed the already reported equilibrium of Z- and E-conformers; their population depends sensitively on solvent.