The title mol­ecule, C12H10N2O3S, is nonplanar with an inter­planar angle of 33.44 (7)° between the benzene and thio­phene rings. In the crystal there exist only weak inter­molecular C—H⋯O inter­actions, π–π inter­actions between the benzene rings [centroid–centroid distance = 3.7465 (14) Å] and X—Y⋯π inter­actions to the thio­phene and benzene rings [N⋯centroid distances = 3.718 (3) and 3.355 (3) Å, respectively]. Inter­molecular C—H⋯O inter­actions link the mol­ecules into chains parallel to the a axis.

In the title compound, C12H10N2O3S, the dihedral angle between the benzene and thio­phene rings is 43.17 (4)°. The crystal structure is devoid of any hydrogen-bonding inter­actions. However, π–π inter­actions between the benzene and thio­phene rings [distance between ring centroids = 3.6850 (11) Å] stack the mol­ecules along the a axis. The absolute structure could not be determined as the crystal studied was a racemic twin with a BASF parameter of 0.31 (6).

In the title Schiff-base type compound, C18H13N3O5, the central furan ring makes dihedral angles of 12.80 (7) and 51.43 (4)° with the terminal benzene rings. The dihedral angle between the benzene rings is 45.43 (3)°. In the crystal, C—H⋯O hydrogen bonds link the mol­ecules into layers parallel to (010). In addition, there are π–π stacking inter­actions within the layer [centroid–centroid distance = 3.584 (1) Å] and between the layers [centroid–centroid distance 3.751 (1) Å].

The title compound, C23H16N2OS, is not planar, the phenyl ring of the benzoyl group making a dihedral of 77.61 (7)° with the benzothio­phene system ring. The benzothio­phene system and the remaining phenyl ring make an angle of 12.71 (13)°. The conformation around the imine functions is E for the C=N bond towards the benzothio­phene system and Z for the C=N bond towards the benzoyl group. The packing of the mol­ecules shows C—H⋯π inter­actions. A weak intramolecular C—H⋯N bond also occurs.

In the crystal structure of the title compound, C12H10N2O2S, the benzene and the 2-nitro­thio­phene rings make a dihedral angle of 7.47 (12)°. The dihedral angle between the nitro group and the attached ring is 1.9 (6)°.

The title Schiff base, C17H19IN2O, is not planar, displaying a dihedral angle of 34.9 (2)° between the two aromatic rings. The mol­ecular conformation allows the formation of a strong intra­molecular O—H⋯N hydrogen bond with graph-set motif S(6) between the hy­droxy group and the imine N atom.

The title Schiff base, C19H24N2O3, exists in the crystal structure in the phenol–imine tautomeric form with an intra­molecular O—H⋯N hydrogen bond. The planes of the aromatic rings form a dihedral angle of 36.8 (8)°. The crystal packing is characterized by C—H⋯O hydrogen bonds and π–π stacking inter­actions [centroid–centroid distance = 3.478 (4)Å].

In the title compound, C6H6N2O3·C8H8O4, the 2-amino-4-nitro­phenol (ANP) and 1-(2,4,6-trihy­droxy­phen­yl)ethanone (THA) mol­ecules are both nearly planar, with r.m.s. deviations of 0.0630 and 0.0313 Å, respectively. The angle between the least-squares planes of THA and ANP is 48.99 (2)°. In THA, an intra­molecular O—H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds lead to the formation of a three-dimensional network. There are also inter­molecular π–π inter­actions between the benzene rings of ANP–ANP and of THA–THA mol­ecules, with centroid–centroid distances of 3.5313 (14) and 3.8440 (16) Å, respectively. Weak C—O⋯π and N—O⋯π inter­actions also occur.

In the title compound, C17H15NS, the benzothio­phene residue and the substituted benzene ring are oriented at a dihedral angle of 61.99 (7)°. An inter­molecular C—H⋯π inter­action contributes to the stability of the crystal structure.

The dihedral angle between the benzene and thio­phene rings in the title compound, C12H10N2O3S, is 27.94 (13)°. An inter­molecular C—H⋯π inter­action contributes to the stability of the crystal structure.

In the title conpound, C16H12N2O2S, the 1-benzothio­phene residue and the substituted benzene ring are oriented at a dihedral angle of 53.36 (6)°. The mol­ecular conformation features a short C—H⋯N contact. There are no significant inter­molecular contacts.

In the title compound, C13H12N2O2S, the dihedral angle between the benzene and thio­phene rings is 36.72 (8)°. An inter­molecular C—H⋯π inter­action contributes to the stability of the crystal structure.

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 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 mol­ecule of the title compound, C13H17N3O4, exists as a zwitterion, with the H atom of the phenol group being transferred to the imine N atom. The C=O, CAr—CAr and C—N bond lengths are in agreement with the oxocyclo­hexa­dienide–iminium zwitterionic form. A strong intra­molecular N+—H⋯O hydrogen bond generates an S(6) ring motif. The morpholine ring adopts a chair conformation. In the crystal, mol­ecules are linked into centrosymmetric dimers by inter­molecular N—H⋯O hydrogen bonds. In addition, C—H⋯O hydrogen bonds and very weak C—H⋯π inter­actions are observed.

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, C15H11Cl2NO2, is a Schiff base which adopts the phenol–imine tautomeric form in the solid state, being stabilized by a strong intra­molecular O—H⋯N hydrogen bond. The mol­ecule is almost planar (r.m.s. deviation for all non-H atoms = 0.049 Å), displaying a dihedral angle of 3.1 (3)° between the planes of the two aromatic rings.

The title compound, C13H10ClNO2, exists in the phenol–imine form in the crystal, and the aromatic rings are oriented at a dihedral angle of 2.82 (9)°. An intra­molecular O—H⋯N hydrogen bond results in the formation of a planar six-membered ring. In the crystal structure, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules into chains.

In the mol­ecule of the title compound, C23H17N3O2, the methoxy­phenyl ring is oriented at dihedral angles of 13.34 (12) and 88.83 (12)° with respect to the methyl­phenyl and phthalonitrile rings, respectively; the dihedral angle between methyl­phenyl and phthalonitrile rings is 89.67 (10)°. In the crystal structure, weak inter­molecular C—H⋯N inter­actions link mol­ecules into chains. A weak C—H⋯π inter­action is also found..

In the title compound, C21H12ClN3O, the phenoxy ring makes dihedral angles of 51.42 (5) and 65.01 (6)°, respectively, with the chlorophenyl and phthalonitrile rings. In the crystal structure, the mol­ecules are inter­linked through weak C—H⋯N and C—H⋯π contacts, and π–π stacking inter­actions via crystallographic inversion centres form a three-dimensional network. The distance between the centroids of the phthalonitrile rings is 3.9104 (11)Å, with a slippage between the rings of 1.626 Å and a perpendicular distance between the rings of 3.556 Å.

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)°.

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.

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 mol­ecule of the title compound, C14H12ClNO, adopts the enol–imine tautomeric form, with an intra­molecular O—H⋯N hydrogen bond. In the mol­ecule, the two benzene rings are twisted with respect to each other by 30.6 (2)°. The crystal structure is stabilized by inter­molecular C—H⋯π inter­actions.