Synthesis and characterization of a series of isoniazid hydrazones. Spectroscopic and theoretical study

A family of hydrazones of isoniazid and a group of hydroxybenzalaldehydes (vanillin, 5-bromovanillin, 5-chlorosalicylaldehyde and 5-bromosalicylaldehyde) were obtained and fully characterized. The results, including theoretical data, are comparatively analyzed along with the already reported hydrazone of o-vanillin. The crystal structures of three compounds were determined. The hydrazones obtained from halogenated aldehydes are isomorphic and chiral to each other. Structures are further stabilized by (pyr) NH+center dot center dot center dot Cl- and OwH center dot center dot center dot Cl- bonds. The vanillin hydrazone shows a conformer that differs from the previously reported. Neighboring molecules are linked to each other through OH center dot center dot center dot N(pyr) bonds, giving rise to a nearly planar polymeric structure. The conformational space was searched and geometries were optimized both in the gas phase and including solvent effects by DFE Results are extended to describe the 5-bromovanillin hydrazone. FTIR, NMR and electronic spectra were measured and assigned with the help of computational calculations. (C) 2016 Elsevier B.V. All rights reserved.