Synthesis, crystal structure and computational studies of a new Schiff base compound: (E)-4-bromo-2-ethoxy-6-{[(2-methoxyphenyl)imino]methyl}phenol

The title compound has enol–imine tautomeric form. E/Z isomerism and enol/keto tautomerism energy barriers have been calculated by relaxed potential energy surface scan calculations with DFT methods.


Computational Studies
Relaxed potential energy surface scan calculations were performed using the DFT/B3LYP/6-311G++(d,p) method with Gaussian 09W software (Frisch et al., 2009) to investigate the connection between the molecular conformation and physical properties of a Schiff base. The results of a torsional angle scan and a proton-transfer scan on the O-HÁ Á ÁN pathway are given in Fig. 4. The torsional barrier between the E/Z isomers was found to be 1.94 kcal mol À1 and the enol-keto tauto-320 Ö zek Yıldırım et al.  Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound, with atom labels and 50% probability displacement ellipsoids for non-H atoms. The dashed line indicates the intramolecular hydrogen bond.
merism barrier was 1.92 kcal mol À1 . The effects of the conformational changes on the aromatic ring can be visualized by calculating HOMA values during the scan calculations. Fig. 5a shows that changes in the HOMA indices are very limited with an average fluctuation of 2%. As can be seen in Fig. 5b, the aromaticity of the C1-C6 ring depends strongly on the prototropic tautomerism.

Synthesis and crystallization
The title compound was prepared by refluxing a mixture of a solution containing 5-bromo-3-ethoxy-2-hydroxybenzaldehyde (0.5 g, 2 mmol) in 20 ml ethanol and a solution containing 2-methoxyaniline (0.25 g, 2 mmol) in 20 ml ethanol. The reaction mixture was stirred for 1 h under reflux. Crystals suitable for X-ray analysis were obtained from an ethanol solution by slow evaporation (yield 70%).

(E)-4-Bromo-2-ethoxy-6-{[(2-methoxyphenyl)imino]methyl}phenol
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.