Crystal and molecular structure of aroyl- and acetylhydrazones of acet- and benzaldehydes

Synthesis and isomerism of hydrazones of 2-(5-thioxo-4,5-dihydro-1,3,4-thiadiazol-2-ylthio)acetohydrazide

“…X-ray spectroscopic studies revealed that in the solid state acyl and aroylhydrazones form only E isomers [9]. It was demonstrated [9] that in the solid state, acylhydrazones of benzaldehyde form syn -conformers that aggregate to centrosymmetric dimers due to their intermolecular hydrogen bonding. Only syn, E -isomers possess C=O and N-N groups in a trans conformation that permits the formation of dimers.…”

“…Only syn, E -isomers possess C=O and N-N groups in a trans conformation that permits the formation of dimers. Calculations performed with the semiempirical MNDO method demonstrated that conjugation effects are also more pronounced in syn, E -isomers compared with anti, E -isomers [9]. In DMSO solutions acyl and aroylhydrazones form mostly (up to 100%) E -isomers [10].…”

“…In solution, the ratio between the anti-and syn -conformers of acylhydrazones depends on the solvent. Because of the high degree of intermolecular hydrogen bonding between the hydrazones, it is expected that in solution acylhydrazones exist mostly as the conglomerates of syn -conformers [9]. Indeed, in non-polar solvents such as chloroform, about 86% of acylhydrazone molecules were found to be in syn -conformer state.…”

“…In contrast, the polar solvent DMSO, which disfavors aggregation of hydrazones through the hydrogen bonding, because of strong competitive interaction with the NH groups, still about 60% of molecules were in syn -conformations [10]. It was shown that aroylhydrazones form only anti -conformers, both, in the solid state [9] and in solution [10].…”

Isatin acylhydrazones with sterically hindered phenolic fragments: synthesis and structures

“…Interest in such compounds is due to their possible use as polyfunctional polymer stabilizers tending toward "intramolecular" synergism. 1 In addition, such compounds are of considerable interest Scheme 1 R = H (1, 4), (2,5) for the study of their biological activity because both isatin hydrazones 2 and sterically hindered phenols 3 find appli cation as drug components.…”