Crystal Structures of the Amide and Iminol Tautomers O-(3,5-dinitrobenzoyloxy)benzohydroxamate. A Case of a Disappearing Solvate?

Abstract

The O-(3,5-dinitrobenzoyl) derivative of benzohydroxamic acid 1 crystallizes in its iminol tautomeric form, hydrogen bonded to a molecule of dimethyl sulfoxide (DMSO) when crystallized from methanol in the presence of DMSO. In contrast, in the absence of DMSO, 1 crystallizes in its amide tautomeric form. Computations suggest that in the absence of DMSO, the amide tautomer of 1 is significantly more stable than the iminol form. Conversely, in the presence of DMSO, the two forms have comparable stabilities. Solution infrared spectra of 1 run in dichloromethane are consistent with the amide tautomeric form predominating; however, titration of aliquots of DMSO results in the formation of a second species with spectral characteristics consistent with the iminol tautomer.