Synthesis, Characterization and Study of E/Z Isomerization in 3-(2-(2,4-Dimethylphenyl) Hydrazono)-6-Fluoroquinolin-(1H, 3H)-2, 4-Dione

The compound 6-fluoro-4-hydroxyquinolin-2(1H)-one (1) was synthesized and reacted with diazotized 2, 4-dimethylaniline in a basic medium, yielding the hydrazone derivative (2) as a deep yellow crystalline compound. The structure of the purified product was confirmed through FT-IR, 1D and 2D NMR, and mass spectroscopic analyses. The results showed that the product exclusively adopts a hydrazone structure, existing as an equilibrium mixture of E and Z geometrical isomers in solution. DFT quantum calculations at the B3LYP/6-311++G (d, p) level indicated that the hydrazone form of compound (2) is more stable than the proposed azo structure, with the Z-hydrazone isomer having the lowest total energy. Additionally, UV-Vis spectroscopy studies of the E and Z isomers of hydrazone compound (2) in solvents of varying polarities showed that the E isomer is the predominant species in non-polar solvents.