The title compound, C₁₆H₂₀N₄O₃S, adopts an L-shaped conformation, as seen by the dihedral angle of 76.93 (7)° formed between the two aromatic rings. The most notable feature of the crystal packing is the formation of N—HO and N—HN hydrogen bonds that lead to supra­molecular chains orientated along the b axis.

The title compound, C₉H₁₀N₂O₃S, is effectively planar, adopts an E conformation about the central C—N bond and exists in the thione form. N—HS and C—HO hydrogen bonds link the mol­ecules into ribbons. Layers of ribbons are connected to adjacent layers via C—HO inter­actions. The crystal is a non-merohedral twin, with the twin law describing a rotation of 180° around the [00] direction.

The crystal structure of the title compound, C₈H₈O₄, is characterized by extensive hydrogen-bonding interactions to yield centrosymmetrically related dimers linked to each other by intermolecular interactions between the hydroxy groups and between the hydroxy and methyl groups.

In the title compound, C₁₁H₆N₂O, the complete mol­ecule is generated by the application of crystallographic twofold symmetry (the mol­ecule is disordered about this axis). The prop-2-yn-1-yl residue is slightly twisted out of the plane of the benzene ring [C—O—C—C torsion angle = 173.1 (3)°] and is orientated away from the nitrile substituents. In the crystal, supra­molecular chains along the a axis, arising from C—HN inter­actions, are connected into stacks along the c axis by π–π inter­actions between the benzene rings [centroid–centroid distance = 3.6978 (6) Å = length of the c axis].

The title compound, C₁₅H₁₁NO, is not planar, as seen in the dihedral angle of 41.92 (12)° formed between the quinoline and phenyl residues. This conformation allows the crystal structure to be stabilized by C—HO inter­actions. Zigzag chains along the a direction, mediated by C—HO inter­actions, may be discerned in the crystal structure and these stack along the c direction, again via C—HO inter­actions. Inter­actions of the type C—Hπ serve to stabilize the zigzag chains and to provide links between them.

In the title compound, C₂₀H₁₂N₂O₂, the phenyl and benzene rings are mutually perpendicular, with the dihedral angle between the phenyl rings being 87.92 (16)° and those formed between the phenyl rings and the benzene rings being 73.68 (15) and 84.65 (15)°. Helical supra­molecular chains along [010], mediated by C—HN inter­actions, are found in the crystal structure.

Photolysis of 9,10-dihydro-9,10[1',2']benzenoanthracene-1',4'-quinone, C₂₀H₁₂O₂, in oxygenated acetone gives the novel photoproduct 9,10-dihydro-9,10-ethanoanthracene-11-one-12-spiro-2'-cyclopent-4'-ene-1',3'- dione, C₂₀H₁₂O₃. The reactant quinone molecule has ideal mm symmetry and lies on a crystallographic mirror plane in Pnma; the photoproduct molecule has ideal m symmetry, which is not utilized in packing in Pna2₁. This product is formed only in the presence of oxygen and a mechanism for its formation is proposed. Unreactivity in attempted solid-state photolysis can be rationalized in terms of crystal packing.

In the title compound, C₈H₃N₃O₂ (systematic name: 4-nitro­benzene-1,2-dicarbo­nitrile), the nitro group is twisted out of the plane of the benzene ring to which it is attached [O—N—C_ring—C_ring torsion angle = 9.80 (13)°]. In the crystal packing, supra­molecular layers with a zigzag topology in the ac plane are sustained by C—HN inter­actions.

In the title compound, C₈H₇N₃O₄ (systematic name: 4-nitro­benzene-1,2-dicarboxamide), each of the substituents is twisted out of the plane of the benzene ring to which it is attached [dihedral angles of 11.36 (2)° for the nitro group, and 60.89 (6) and 34.39 (6)° for the amide groups]. The amide groups are orientated to either side of the least-squares plane through the benzene ring with the amine groups being directed furthest apart. In the crystal, a three-dimensional architecture is established by a network of N—HO hydrogen bonds.

In the title compound, C₁₁H₆N₂O {systematic name: 3-(prop-2-yn-1-yl­oxy)benzene-1,2-dicarbo­nitrile}, the 14 non-H atoms are approximately coplanar (r.m.s. deviation = 0.051 Å) with the terminal ethyne group being syn with the adjacent cyano residue. In the crystal, centrosymmetric dimers are connected by pairs of C—HN inter­actions and these are linked into a supra­molecular tape parallel to (1-30) via C—HN inter­actions involving the same N atom as acceptor.