2-[(4-Bromophenyl)iminomethyl]-3,5-dimethoxyphenol

There are two independent molecules in the asymmetric unit of the title compound, C15H14BrNO3, with very similar geometrical parameters. Each molecule adopts the phenol–imine tautomeric form, with strong intramolecular O—H⋯N hydrogen bonds. The two molecules are non-planar, the dihedral angles between the two aromatic rings being are 24.6 (2) and 30.30 (13)°.

There are two independent molecules in the asymmetric unit of the title compound, C 15 H 14 BrNO 3 , with very similar geometrical parameters. Each molecule adopts the phenolimine tautomeric form, with strong intramolecular O-HÁ Á ÁN hydrogen bonds. The two molecules are non-planar, the dihedral angles between the two aromatic rings being are 24.6 (2) and 30.30 (13) . H atoms treated by a mixture of independent and constrained refinement Á max = 0.61 e Å À3 Á min = À0.92 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). supporting information ). E65, o934 [doi:10.1107
The overall behaviour of these compounds has been ascribed to a proton-transfer reaction between a phenol-imine and a keto-amine tautomer. It is claimed that phenol-imine tautomerism is dominant in salicylaldimine, while the keto-amine form is preferred in naphthaldimine Schiff bases, depending on the solvent polarities. Our X-ray investigation of the title compound has indicated that the phenol-imine tautomer is favoured over the keto-amine tautomer.
An ORTEP view of the molecule is shown in Fig. 1. There are two independent molecules in the asymmetric unit which have very similar geometrical parameters. Both molecules adopt the phenol-imine tautomeric form and have a strong intramolecular O-H···N hydrogen bond whose details are given in Table 1. The C7-N1 [1.296 (4) Å] and C22-N2

S3. Refinement
All H atoms bonded to C were positioned geometrically and treated using a riding model, fixing the bond lengths at 0.93 and 0.96 Å for C amoatic -H or C methyl H, respectively. The displacement parameters of the H atoms were constrained as U iso (H) = 1.2U eq (C aromatic ) or 1.5U eq (C methyl ). The positions of the hydroxyl H atoms were obtained from an electron density difference map and were refined freely.  The molecular structure of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are at the 50% probability level Dashed lines indicate intramolecular hydrogen bond.

Figure 2
The crystal packing of the title compound. Dashed lines indicate intramolecular hydrogen bond.

Special details
Experimental. 360 frames, detector distance = 100 mm Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.