Infrared absorption spectra of 2-(hydroxyimino)propanohydroxamic and oxalodihydroxamic acids isolated in argon matrices

Abstract

For the first time, infrared spectra of 2-(hydroxyimino)propanohydroxamic acid (hpha) and oxalodihydroxamic acid (oxha) isolated in argon matrices at 15–18 K have been recorded. The interpretation of the spectra has been aided by DFT and MP2 calculations of possible structural isomers. Calculations were performed on the relative isomeric abundances of these compounds, with different conformations around the C–C and the hydroxamic C–N bonds, and with different configurations around the oximic C–N bonds. Although the computations suggested the presence of other isomers in the matrix-isolated spectra, only the most stable isomer was observed for hpha and oxha. The optimized geometries for both compounds show a preference for the keto form, with entgegen and zusammen arrangements around the C–C and the C–N hydroxamic bonds, respectively. The B3LYP/6-31G(d) level of theory is shown to predict the experimental spectra quite well.