In the indane ring system of the title mol­ecule, C13H12O4, the hy­droxy-bearing C atom is 0.134 (1) Å out of the plane of the remaining essentially planar atoms (r.m.s. deviation = 0.010 Å). In the crystal, mol­ecules are linked into chains along the b axis by inter­molecular O—H⋯O hydrogen bonds. Additional stabilization is provided by weak inter­molecular C—H⋯O hydrogen bonds.

In the title compound, C8H7N3O2·H2O, the 2-methyl-5-nitro-1H-benzimidazole mol­ecule, excluding the methyl H atoms, is approximately planar, with a maximum deviation of 0.137 (1) Å. The crystal structure is stabilized by water mol­ecules via N—H⋯O(water), O(water)—H⋯O and O(water)—H⋯N hydrogen bonds, forming sheets parallel to the (100) plane. A short inter­molecular contact between the benzene and imidazole rings, with a centroid–centroid distance of 3.6419 (10) Å, indicates a π–π inter­action.

In the title mol­ecule, C10H8N2O4, the imidazolidine ring adopts a twisted conformation. In the crystal, the mol­ecules are linked via a pair of bifurcated inter­molecular O—H⋯O hydrogen bonds, forming an inversion dimer. The dimers are further linked via N—H⋯O hydrogen bonds into a tape along the b axis.

In the title compound, C21H22O5, the mean planes of the pyran and dimeth­oxy­phenyl rings are nearly perpendicular to one another, with the dihedral angle between them being 88.21 (8)°. The pyran ring adopts a boat conformation whereas the two fused cyclo­hexane rings adopt envelope conformations. In the crystal, mol­ecules are linked into a three-dimensional network by inter­molecular C—H⋯O hydrogen bonds.

The asymmetric unit of the title compound, C27H46, contains two crytallographically independent cholest-5-ene mol­ecules (A and B). In each mol­ecule, the three six-membered rings are all in chair conformations, while the five-membered ring is in a twist conformation. The terminal isopropyl group of mol­ecule A has a (−)-gauche conformation, whereas that of mol­ecule B has a (+)-gauche conformation. No significant inter­molecular inter­actions are observed in the crystal structure.

The asymmetric unit of the title compound, C14H17N3O3·0.25H2O, comprises two independent organic mol­ecules and a water mol­ecule lying on a crystallographic twofold rotation axis with 50% site occupancy. In both independent mol­ecules, the cyclo­hexene rings adopt envelope conformations but superposition of the two molecules shows that the flap atoms point in opposite directions. In the crystal, N—H⋯O and C—H⋯O hydrogen bonds inter­connect adjacent mol­ecules into a three-dimensional network. Weak inter­molecular π–π aromatic stacking inter­actions [centroid–centroid distances = 3.4985 (9) and 3.6630 (9) Å] are also observed.

The asymmetric unit of the title quinoxaline compound, C10H9N3O2, contains two crystallographically independent mol­ecules (A and B). The quinoxaline ring systems are essentially planar, with maximum deviations of 0.006 (1) and 0.017 (1) Å, respectively, for mol­ecules A and B. In mol­ecule A, the dihedral angle formed between the quinoxaline ring system and nitro group is 10.94 (3)° [6.31 (13)° for mol­ecule B]. In the crystal, mol­ecules are linked into chains propagating along [001]: one forms zigzag chains linked by C—H⋯O hydrogen bonds, whilst the other forms ladder-like chains by way of C—H⋯N and C—H⋯O hydrogen bonds. The packing is further consolidated by weak π–π inter­actions [range of centroid–centroid distances = 3.5895 (7)–3.6324 (7) Å].

In the title compound, C14H18N2O, the benzimidazole grouping is close to planar, with a maximum deviation of 0.042 Å; the six-membered non-aromatic ring adopts an envelope conformation. In the crystal structure, mol­ecules are linked into infinite sheets lying parallel to the bc plane by O—H⋯N and C—H⋯O hydrogen bonds.

In the deca­hydro­phenanthrenone ring system of the title compound, C27H44O, the two cyclo­hexane rings adopt chair conformations, whereas the cyclo­hexene ring adopts an envelope conformation. The cyclo­pentane ring is twisted. In the crystal structure, mol­ecules are stacked along the a axis, but no significant inter­molecular inter­actions are observed.

In the title compound, C15H8N2O, the fused ring system is approximately planar, with a maximum deviation of 0.039 (1) Å. In the crystal, weak inter­molecular C—H⋯O inter­actions help to establish the packing.

The title compound, C27H43ClO, is a steroid derivative composed of a saturated carbon fused-ring framework with an alkyl side chain. The A and C rings have chair conformations and the B and D rings assume half-chair conformations. The cholesterol side chain is fully extended with a gauche, trans conformation of the terminal methyl groups. In the crystal structure, the molecules are aligned in an antiparallel fashion, forming alternate layers. These layers are then linked via C—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title compound, C34H51NO2, the dihedral angle between the planes of the phenyl ring and the carbonyl group is 9.30 (2)°. No significant inter­molecular inter­actions are observed in the crystal structure. The C5H11 fragment is disordered over two positions with site occupancies of 0.611 (6) and 0.389 (6).

The crystal structure of the title compound, C15H14O6·H2O, has been redetermined from single-crystal X-ray data. The structure was originally determined by Peet et al. [J. Heterocycl. Chem. (1995), 32, 33–41] but the atomic coordinates were not reported or deposited in the Cambridge Structural Database. The ethyl substituent is disordered over two sites with refined occupancies of 0.815 (6) and 0.185 (6). The indeno group is almost planar [maximum deviation 0.0922 (14) Å] and makes an angle of 68.81 (4)° with the furan ring. The fused ring molecules are assembled in pairs by intermolecular O—H⋯O hydrogen bonds. The resulting dimers are also hydrogen bonded to the water molecules, forming double-stranded chains running along the a axis.