Collect. Czech. Chem. Commun. 1981, 46, 729-739

Dipole moments of hydroxamic acids and N,O-diacylhydroxylamines

Aleksandr I. Artemenkoa, Inga V. Tikunovaa, Evgenii K. Anufrieva, Václav Jehličkab and Otto Exnerc

a Department of Organic and Analytical Chemistry, Belgorod Technological Institute of Building Materials, Belgorod, 308 600 U.S.S.R.
b Department of Physical Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6
c Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6, Czechoslovakia


Dipole moments of nine aromatic hydroxamic acids Ia-Ii and of nine N,O-diacylhydroxylamines IIa-IIi were measured in dioxan solution. The results for hydroxamic acids are interpreted in terms of the Zsp conformation (A) with an intramolecular hydrogen bond contributing considerably to the total dipole moment; the conformation is similar to that of peroxy acids but the hydrogen bond is weaker. A similar interpretation is possible for N-phenylbenzhydroxamic acids using the dipole moment data from the literature. New data for N,O-diacylhydroxylamine agree with the previously established nonplanar conformation (L). If axially unsymetrical aryl groups are present, they take one of the two coplanar positions independently of the other moiety; hence the effective dipole moments do not differ too much from the assumption of a statistical population of all conformations.