In the title compound, C(12)H(12)N(2)O(3), the five-membered ring attached to the aromatic ring adopts an envelope conformation with a C atom in the flap position. The spiro-linked five-membered ring adopts a twisted conformation. In the crystal, C-H⋯O hydrogen bonds link the mol-ecules into C(5) chains propagating in [001].

The asymmetric unit of the title compound, C(12)H(12)O(5), contains two independent mol-ecules. In each, the 1,3-dioxane ring adopts an envelope conformation with the dimethyl-substituted C atom forming the flap. The crystal structure is stabilized by weak inter-molecular C-H⋯O hydrogen bonds.

In the title compound, C(23)H(23)NO(5), the C(5)N ring adopts an envelope conformation with a C atom as the flap, whilst the saturated C(6) ring fused to it adopts a chair conformation. In the crystal, inversion dimers linked by pairs of N-H⋯O hydrogen bonds generate R(2) (2)(8) loops.

In the title compound, C(25)H(32)O(5), the two cyclo-hexenone rings have envelope conformations with the C atom bearing two methyl groups as the flap atom in each ring. Relatively strong intra-molecular O-H⋯O hydrogen bonds are observed.

In the title compound, C(38)H(31)ClN(2)O(4), the isoxazole ring adopts an envelope conformation with the N atom as the flap. The crystal packing is stabilized by C-H⋯O hydrogen bonds, forming chains running along the c-axis direction.

In the title compound, C(18)H(18)O(4), the 1,3-dioxane ring adopts a distorted envelope conformation with the C atom common to the cyclo-hexane ring forming the flap. In the crystal, inversion dimers linked by pairs of C-H⋯O hydrogen bonds occur.

In the title compound, C(15)H(15)NO(5), the six-membered dioxane ring assumes an envelope conformation with the dimethyl substituted C atom as the flap atom. An intra-molecular N-H⋯O inter-action is also present. In the crystal structure the mol-ecules are linked via C-H⋯O hydrogen bonds into supra-molecular chains along the b axis.

In the title compound, C(18)H(20), the five-membered ring of the indane fragment adopts an envelope conformation, with the flap atom deviating by 0.399 (3) Å from the plane of the remaining four atoms. The dihedral angle between the phenyl ring and the indane benzene ring is 79.58 (7)°.

In the title compound, C8H7FO2S, the thio-phene ring has an envelope conformation, with the S atom bearing the two O atoms being the flap. In the crystal, mol-ecules are linked by C-H⋯O and C-H⋯F inter-actions, generating a three-dimensional network structure.

The title compound (OctaInd), C(18)H(12)Br(8), is a commercial brominated flame retardant (BFR). In the mol-ecule, the five-membered ring has a slight envelope conformation, with a deviation of 0.317 (9) Å for the flap C atom from four essentially planar C atoms. The dihedral angle between the two benzene rings is 74.00 (16) Å.