Synthesis, crystal structures and tautomerism in novel oximes based on hydroxyalkylpyrazolones

New Look on 3-Hydroxyiminoflavanone and Its Palladium(II) Complex: Crystallographic and Spectroscopic Studies, Theoretical Calculations and Cytotoxic Activity

“…That suggests that the initial form 1 takes after dissolution in chloroform is 3Z-HIF. This has been confirmed by Enchev et al [33] in the case of 4-nitroso-5-pyrazolones, and by Belmar et al [32] in the case of 1-(2-hydroxyethyl)-3-methyl-4-hydroxyimino-5-pyrazolone, where a polar solvent (DMSO) supports the formation of the E diastereoisomer, and a non-polar solvent, i.e., chloroform, supports the formation of the Z form. Enchev et al [34] describe the tautomeric and conformational equilibrium of 9,10-phenantrenequinonemonooxime, where the most prevalent form of the molecule in chloroform is the Z isomer, and in DMSO the E isomer.…”

“…In the case of 3-HIF, the existence of the nitroso-enol tautomer is not supported by the data. 13 C-NMR spectra recorded in DMSO-d6 and CDCl3 reveal a signal assigned to the carbonyl carbon atom near 177 ppm ( Figure S5 in Supplementary Materials), which is typical for carbonyl carbon atoms C=O [31,32]. Signals from C-OH carbon atoms should be right-shifted towards around 160 ppm [32,35].…”

“…However, our results differ regarding the significance of the observed downfield shift of the oxime proton signal: while Kostka and Zyner [13] suggest that the shift indicates 3Z(syn) geometry of the molecule, our results indicate that the ligand exists as an E (anti) isomer rather than Z (syn), both in solid form and in DMSO solution. The downfield-shifted signal of the oxime proton is not necessarily due to the presence of an intramolecular hydrogen bond in 3Z(syn)-HIF [13], but it is typical for the oxime proton in similar molecules [31][32][33]. Additionally, the signals of aromatic protons from the phenyl ring B of the flavanone moiety are split in two parts (7.24-7.28 ppm for the 2H bound to the ortho carbon atoms, and 7.30-7.38 ppm for the 3H bound to the meta and para carbon atoms, ring C), which indicates the presence of steric interaction between the phenyl group and the oxime -OH group in the anti position.…”

Synthesis and Characterization of Phenylene‐bis‐pyrazolones and Nitrosation Derivatives

“…Once again, even the IR information is interesting to analyze; it is not enough to fully establish which structure prevails in solid phase. However, under the light of previous reports and X‐ray diffraction preliminary results, the bis ‐keto‐oximino tautomers ( IX ) for 3a and 4a seem to be quite likely .…”

Amidoximes and Oximes: Synthesis, Structure, and Their Key Role as NO Donors

“…Recently, Lopez et al demonstrated by theoretical calculations that this isomerization occurs via a bimolecular mechanism involving two oximes or two nitrones [23]. Previous studies suggested that the oxime–nitrone tautomerism likely originated from a thermal 1,2-hydrogen shift and a solvation effect [25,26,27,28].…”