A comparative study on 4-(4-(3-mesityl-3-methylcyclobutyl)thiazole-2-yl)-1-thia-4-azaspiro[4.5]decan-3-one: Experimental and density functional methods

Synthesis, crystal structure, Hirshfeld surface investigation and comparative DFT studies of ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate

The ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate (1), a thiazole ester, was synthesized by refluxing 1-(2-nitrobenzylidene)thiosemicarbazide and ethyl bromopyruvate. The compound is characterized by spectrometric, spectroscopic and single crystal (SC-XRD) techniques. Non-covalent interactions that are responsible for crystal packing are explored by Hirshfeld surface analysis. All theoretical calculations were performed by DFT quantum chemical methods using 6-311G(d,p) and cc-pVTZ basis sets and compared. Theoretical harmonic frequencies of ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate (1) were optimized. Confirmation of hydrogen bonding sites was analyzed by molecular electrostatic potential (MEP) and Mulliken population analysis. The vibrational frequencies of characteristic functional groups and chemical shifts were found in good agreement with experimental assignments. Frontier molecular orbital (FMO) revealed relatively small HOMO–LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gape, which speaks off the nearly planar geometry and extended conjugation, as compared to the substituents with no conjugation possible. It has also been observed that –NO₂ substituent plays a vital role for this relatively small HOMO–LUMO gape and overall electronic properties when compared with similar thiazole carboxylates (2–6, Table 6). Ethyl 2-[2-(2-nitrobenzylidene)hydrazinyl]thiazole-4-carboxylate (1) was also evaluated for its anti-oxidant and anti-microbial activities.

Crystal structure and Hirshfeld surface analysis of (Z)-4-{[4-(3-methyl-3-phenyl-cyclo-but-yl)thia-zol-2-yl]amino}-4-oxobut-2-enoic acid

The title cyclo-butyl compound, C18H18N2O3S, was synthesized by the inter-action of 4-(3-methyl-3-phenyl-cyclo-but-yl)thia-zol-2-amine and maleic anhydride, and crystallizes in the ortho-rhom-bic space group P212121 with Z' = 1. The mol-ecular geometry is partially stabilized by an intra-molecular N-H⋯O hydrogen bond forming an S 1 1(7) ring motif. The mol-ecule is non-planar with a dihedral angle of 88.29 (11)° between the thia-zole and benzene rings. In the crystal, the mol-ecules are linked by O-H⋯N hydrogen bonds, forming supra-molecular ribbons with C 1 1(9) chain motifs. To further analyze the inter-molecular inter-actions, a Hirshfeld surface analysis was performed. The results indicate that the most important contributions to the overall surface are from H⋯H (43%), C⋯H (18%), O⋯H (17%) and N⋯H (6%), inter-actions.

Structural and spectroscopic characterization of 4-(3-methyl-3-phenylcyclobutyl)-2-(2-propylidenehydrazinyl)thiazole: A combined experimental and DFT analysis

We investigated the structural and spectroscopic properties of the title compound by means of experimental and DFT quantum chemical methods. The crystal structure of compound was brought to light by single crystal X-ray diffraction method, and were characterized spectroscopically using FT-IR and NMR spectra. FT-IR spectrum in solid state was observed in the region 4000-400 cm(-1). The (1)H and (13)C NMR spectra were recorded in CDCl3 solution. The molecular geometry were those obtained from the X-ray structure determination was optimized using density functional theory (DFT/B3LYP) method with the 6-31G(d, p) and 6-31+G(d, p) basis sets in ground state. From the optimized geometry of the molecule, geometric parameters (bond lengths, bond angles, torsion angles), vibrational assignments and chemical shifts of the title compound have been calculated theoretically and compared with the experimental data. Although theoretical calculations were carried out in gas phase, no significant differences in these values.