(E)-2-{[(2-Aminophenyl)imino]methyl}-5-(benzyloxy)phenol and (Z)-3-benzyloxy-6-{[(5-chloro-2-hydroxyphenyl)amino]methylidene}cyclohexa-2,4-dien-1-one

Abstract

The title Schiff base compounds, C20H18N2O2 (I) and C20H16ClNO3 (II), were synthesized from 4-benzyloxy-2-hydroxybenzaldehyde by reaction with 1,2-diaminobenzene for (I), and condensation with 2-amino-4-chlorophenol for (II). Compound (I) adopts the enol–imine tautomeric form with an E configuration about the C=N imine bond. In contrast, the o-hydroxy Schiff base (II), is in the keto–imine tautomeric form with a Z configuration about the CH—NH bond. Neither molecule is planar. In (I), the central benzene ring makes dihedral angles of 46.80 (10) and 78.19 (10)° with the outer phenylamine and phenyl rings, respectively, while for (II), the corresponding angles are 5.11 (9) and 58.42 (11)°, respectively. The molecular structures of both compounds are affected by the formation of intramolecular contacts, an O—H...N hydrogen bond for (I) and an N—H...O hydrogen bond for (II); each contact generates an S(6) ring motif. In the crystal of (I), strong N—H...O hydrogen bonds form zigzag chains of molecules along the b-axis direction. Molecules are further linked by C—H...π interactions and offset π–π contacts and these combine to form a three-dimensional network. The density functional theory (DFT) optimized structure of compound (II), at the B3LYP/6–311+G(d) level, confirmed that the keto tautomeric form of the compound, as found in the structure determination, is the lowest energy form. The antioxidant capacities of both compounds were determined by the cupric reducing antioxidant capacity (CUPRAC) process.

Keywords

• crystal structure
• Schiff base
• CUPRAC
• antioxidant capacity
• DFT calculations