Keto-enol tautomerism of (E)-2-[(3,4-dimethylphenylimino)methyl]-4-nitrophenol: Synthesis, X-ray, FT-IR, UV–Vis, NMR and quantum chemical characterizations

• A new Schiff base compound has been synthesized.
• Single crystal XRD, FT-IR, UV–Vis, NMR and computational studies were given.
• Theoretical calculations were performed with Gaussian and Slater type orbitals.
• The keto character of the compound increases with the increasing solvent polarity.

(E)-2-((3,4-dimethylphenylimino)methyl)-4-nitrophenol, which is a new Schiff base compound, was synthesized and characterized by experimental and computational methods. Molecular geometry, harmonic oscillator model of aromaticity (HOMA) indices, intra- and inter-molecular interactions in the crystal structure were determined by using single crystal X-ray diffraction technique. The optimized structures, which are obtained by Gaussian and Slater type orbitals, were compared to experimental structures to determine how much correlation is found between the experimental and the calculated properties. Intramolecular and hyperconjugative interactions of bonds have been found by Natural Bond Orbital analysis. The experimental infrared spectrum of the compound has been analyzed in detail by the calculated infrared spectra and Potential Energy Distribution analysis. To find out about the correlation between the solvent polarity and the enol-keto equilibrium, experimental UV–Visible spectra of the compound were obtained in benzene, CHCl3, EtOH and DMSO solvents. In these solvents, the UV–Vis spectra and relaxed potential energy surface scan (PES) calculations have been performed to get more insight into the equilibrium dynamics. Solvent effects in UV–Vis and PES calculations have been taken into account by using Polarizable Continuum Modelling method. 1H and 13C NMR spectra of the compound (in DMSO) were analyzed. The computational study of nonlinear optical properties shows that the compound can be used for the development of nonlinear optical materials.

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