| Summary: | 11<i>H</i>-Indeno[1,2-<i>b</i>]quinoxalin-11-one oxime (<b>IQ-1</b>) and tryptanthrin-6-oxime are potent c-Jun N-terminal kinase 3 (JNK-3) inhibitors demonstrating neuroprotective, anti-inflammatory and anti-arthritic activity. However, the stereochemical configuration of the oxime carbon–nitrogen double bond (<i>E</i>- or <i>Z</i>-) in these compounds was so far unknown. In this contribution, we report the results of the determination of the double bond configuration in the solid state by single crystal X-ray diffraction and in solution by 1D and 2D NMR techniques and DFT calculations. It was found that both in the solid state and in solution, <b>IQ-1</b> adopts the <i>E</i>-configuration stabilized by intermolecular hydrogen bonds, in contrast to previously assumed <i>Z</i>-configuration that could be stabilized only by an intramolecular hydrogen bond.
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