1-[(E)-(2-Phenoxyanilino)methylene]naphthalen-2(1H)-one

The molecule of the title compound, C23H17NO2, a Schiff base derived from 2-hydroxy-1-naphthaldehyde, crystallizes in the keto–amine tautomeric form. The dihedral angle between the aniline and hydroxybenzene rings is 77.41 (17)°, whereas the planes of the naphthaldehyde and fused aniline benzene rings are nearly coplanar, making a dihedral angle of 8.29 (15)°. Intramolecular N—H⋯O hydrogen bonding, a characteristic hydrogen bond for Schiff bases, helps to stabilize the molecular structure. Weak intermolecular C—H⋯π interactions are present in the crystal structure.

The molecule of the title compound, C 23 H 17 NO 2 , a Schiff base derived from 2-hydroxy-1-naphthaldehyde, crystallizes in the keto-amine tautomeric form. The dihedral angle between the aniline and hydroxybenzene rings is 77.41 (17) , whereas the planes of the naphthaldehyde and fused aniline benzene rings are nearly coplanar, making a dihedral angle of 8.29 (15) . Intramolecular N-HÁ Á ÁO hydrogen bonding, a characteristic hydrogen bond for Schiff bases, helps to stabilize the molecular structure. Weak intermolecular C-HÁ Á Á interactions are present in the crystal structure.
The structure of o-hydroxy aromatic Schiff base has drawn attention due to their keto-enol tautomerism in recent years (Hadjoudis et al., 1987). As being characteristic feature of Schiff bases there are two alternative intra-molecular hydrogen bonds depending on the type of tautomer. The structure with intra-molecular N-H···O hydrogen bond is called keto tautomer. The enol tautomer is, on the other hand, a structure involving O-H···N type hydrogen bond (Caligaris & Randaccio et al., 1987). Details of hydrogen bond geometry are given in Table 1.
The proton transfer responsible for the tautomerization requires a small amount of energy which can be obtained by temperature change or light (Caligaris & Randaccio et al., 1987). The proton transfer reaction causes the bond distances to deviate from the ideal value 1.338 Å, which leads to a decrease in aromaticity of the ring. In order to investigate deformation in π-electron delocalization of aromatic rings, HOMA (Harmonic Oscillator Model of Aromaticity) index is a useful tool. The HOMA index is equal to unity for purely aromatic systems and zero for non-aromatic systems (Krygowski et al., 1993). The HOMA index of the naphthalene ring of (I) was calculated as 0.670, which is fairly less than the HOMA index of aromatic naphthalene. It can be inferred that π-electron delocalization of the ring involving proton transfer is considerably deformed.
The molecule of (I) is generated by connecting 2-phenoxyaniline and naphthaldehyde units through a nitrogen bridge ( Figure 1). Rings A(C1-C6), B(C7-C12) and C(C14-C23) are planar and the dihedral angles between them are A/ B=77.41 (17)°, A/C=79.24 (15)°, B/C=8.29 (15)°. The hydrogen atom in the title compound (I) is located on nitrogen atom, thus the keto-amine tautomer is favored over the phenol-imine form. The presence of keto form can be also confirmed by N1-C13 and C15-O1 bond lengths. The C15-O1 bond length of 1.276 (7)Å indicates double-bond character while the N1-C13 bond length of 1.315 (6)Å indicates single-bond character. Similar results are also reported in the literature (Özek et al., 2004;Takano et al., 2009]. Intermolecular weak C-H···π ring interactions are also present in the crystal structure ( Figure 2). Details of C-H···π contacts are given in Table 1. supplementary materials sup-2 Refinement H atoms attached to carbon atoms were placed in calculated positions with U iso (H) = 1.2U eq (C). The coordinates of the amine hydrogen obtained from a difference map and refined isotropically with N-H = 0.86Å constrain. Fig. 1. The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability.

Special details
Experimental. 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.
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.
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 Rfactors(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.