The structural study of acetohydroxamic and oxalodihydroxamic acids in DMSO solution based on the DFT calculations of NMR spectra

The 1H and 13C NMR spectra of acetohydroxamic (aha) and oxalodihydroxamic (oxha) acids were measured in DMSO-d6 solution. The atoms chemical shifts of chosen stable entgegen and zusammen conformers of monomeric acids were computed along with some clusters of the compounds with the solvent molecules [B3LYP/6-311þþG(d,p), GIAO]. The latter were proposed to explain the differences between the theoretical and experimental resonances of the protons of the N–H and O–H groups. The computed chemical shifts of aha-(DMSO)2 and oxha-(DMSO)2 models are in good agreement with experimental data proving that the compounds existing in solution form aggregates with DMSO. The acids are H-bonded via all the labile protons to the oxygen atoms of the solvent molecules. aha exists in the zusammen and entgegen (relative to C–N bond) forms with the relative intensities of 8:1 while the sole z,E,z-conformers (notation refers to C–N, C–C and C–N bonds, respectively) were found for oxha. q 2004 Elsevier B.V. All rights reserved.