Tautomeric properties, conformations and structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine

• Published in: Journal of molecular structure 1999-11, Vol.510 (1), p.207-214
• Main Authors: Elmali, A., Kabak, M., Kavlakoglu, E., Elerman, Y., Durlu, T.N.
• Format: Article
• Language: English
• Subjects: AM1; Schiff base; Tautomerism; Thermochromic; X-ray
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/S0022-2860(99)00074-5

The crystal structure of N-(2-hydroxy-5-chlorophenyl) salicylaldimine (C 13H 10NO 2Cl) was determined by X-ray analysis. It crystallizes orthorhombic space group P2 12 12 1 with a=12.967(2) Å, b=14.438(3) Å, c=6.231(3) Å, V=1166.5(6) Å 3, Z=4, D c=1.41 g cm −3 and μ(MoK α)=0.315 mm −1. The title compound is thermochromic and the molecule is nearly planar. Both tautomeric forms (keto and enol forms in 68(3) and 32(3)%, respectively) are present in the solid state. The molecules contain strong intramolecular hydrogen bonds, N1–H1⋯O1/O2 (2.515(1) and 2.581(2) Å) for the keto form and O1–H01⋯N1 for the enol one. There is also strong intermolecular O2–H⋯O1 hydrogen bonding (2.599(2) Å) between neighbouring molecules. Minimum energy conformations AM1 were calculated as a function of the three torsion angles, θ 1(N1–C7–C6–C5), θ 2(C8–N1–C7–C6) and θ 3(C9–C8–N1–C7), varied every 10°. Although the molecule is nearly planar, the AM1 optimized geometry of the title compound is not planar. The non-planar conformation of the title compound corresponding to the optimized X-ray structure is the most stable conformation in all calculations.