Collect. Czech. Chem. Commun. 1979, 44, 895-907

The conformation of substituted hydroxyureas and hydroxythioureas in solution

Jiří Mollina, Pavel Fiedlerb, Václav Jehličkac and Otto Exnerb

a Department of Inorganic and Physical Chemistry, Faculty of Natural Sciences, Palacký University, 771 46 Olomouc
b Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6
c Department of Physical Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6


The conformation of 1,3-disubstituted 1-hydroxyureas Ia-d and 1-hydroxythioureas IIa-d, mostly with aromatic substituents, was investigated by means of dipole moments in dioxan solution and by infrared spectroscopy. The results are concordant for the two classes of compounds. The most populated conformation is near to the planar Z, E, ap form (A), or possibly with the hydroxyl hydrogen out of the N-C-N-O plane (between A and B). This finding from the analysis of dipole moments is corroborated by the presence of the amide-II band and absence of intramolecular hydrogen bonds. While the conformation of hydroxyureas seems to be virtually uniform, in the case of hydroxythioureas a less abundant rotamer may be present in nonpolar solvents, possibly the E, E, sp (G) or E, E, ap (F) form. The conformation found (A) is not explicable in terms of hydrogen bonds and/or steric factors when compared to symmetrically substituted ureas (thioureas) and to N-alkylhydroxamic acids.