The Schiff base compound, N-n-Decyl-2-oxo-5-nitro-1-benzylidene-methylamine, has been -synthesized and characterized by IR, electronic spectroscopy, and X-ray single-crystal determination. Molecular geometry from X-ray experiment of the title compound in the ground state have been compared using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-31G(d) basis set. Calculated results show that density functional theory (DFT) at B3LYP/6-31G(d) level can well reproduce the structure of the title compound. To investigate the solvent effect for the atomic charge distributions of the title compound, self-consistent reaction field theory with Onsager reaction field model was used. In addition, DFT calculations of the title compound, molecular electrostatic potential and thermodynamic properties were performed at B3LYP/6-31G(d) level of theory.

X-ray analysis reveals that the title Schiff base compound, C17H19NO3, possesses both OH and NH tautomeric character in its mol­ecular structure. The occupancies of the enol and keto tautomers are 0.62 (3) and 0.38 (3), respectively. The presence of the minor keto form could not be confirmed from the IR spectrum. The mol­ecule is approximately planar, the dihedral angle between the planes of the two aromatic rings being 6.97 (8)°. The mol­ecular structure of the major component is stabilized by an intra­molecular O—H⋯N hydrogen bond, which generates an S(6) ring motif (N—H⋯O hydrogen bond in the minor component).

The title compound, C16H17NO, is a Schiff base which adopts the phenol–imine tautomeric form in the solid state. The mol­ecule is almost planar, with a dihedral angle of 4.61 (4)° between the aromatic rings. The molecular structure is stabilized by an intramolecular O—H⋯N hydrogen bond which generates a six membered ring.

The title Schiff base compound, C14H12N2O4, is in an inter­mediate state between NH and OH tautomers. Apart from the intra­molecular O—H⋯N hydrogen bond, there are inter­molecular C—H⋯O hydrogen bonds, generating centrosymmetric R 2 2(18) and R 2 2(14) dimers.

The title compound, C14H11Cl2NO, is a Schiff base which adopts the phenol–imine tautomeric form in the solid state. There are two mol­ecules in the asymmetric unit. Head-to-tail π–π inter­actions [centroid-to-centroid distances of 3.682 (2), 3.708 (2), 3.904 (2) and 3.910 (2) Å] between adjacent mol­ecules produce two symmetry-independent infinite chains running along the b axis.