Experimental and theoretical investigation of the molecular and electronic structure of 3-ethoxy-4-isopropylaminocyclobut-3-ene-1,2-dione.

The title compound, 3-ethoxy-4-isopropylaminocyclobut-3-ene-1,2-dione (EIAC) has been synthesized and characterized by NMR, FT-IR, UV-vis spectroscopy and single-crystal X-ray diffraction. The (1)H NMR spectra were recorded at 300 K and 315 K in CDCl(3) to determine syn/anti conformers of the compound EIAC. Density functional theory (DFT) calculations, optimized geometrical parameters, vibrational frequencies and chemical shift values of syn/anti conformer in CDCl(3) have been performed at B3LYP/6-311G(d) level, and compared with the experimental data. The values provided with the calculations support the experimental data of the compound EIAC. The presence of NH⋯O type intermolecular H bond can be perceived from the difference between experimental calculations and results of FT-IR and NMR calculations. In addition, B3LYP/6-311G(d) basis set has been used to calculate the molecular electrostatic potential, frontier molecular orbitals and electronic absorption spectra. HOMO-LUMO electronic transition of 5.12 eV is derived from the contribution of the bands n→σ(*) or π→π(*). FT-IR, NMR and X-ray spectral results and additionally DFT calculations exhibit that the compound EIAC exists in keto-enamine tautomeric form. The experimental (1)H NMR spectra recorded at 300 K and 315 K and theoretical (1)H NMR data indicate that the compound EIAC is in syn conformer.