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In both title compounds, C(19)H(24)N(2)O(2), (I), and C(17)H(21)N(3)O(2), (II), respectively, there are two molecules in the asymmetric unit and the pyrrolidine rings adopt envelope conformations. The conformations of the cyclooctane [in (I)] and 1-methylpiperidone [in (II)] rings are boat-chair and chair, respectively. The indolin-2-one group is almost perpendicular to the pyrrolidine ring. Intermolecular C-H...O, N-H...O and N-H...N interactions provide stability to the structures.

The crystal structures of endo,endo-2,5-dibromo-9-oxabicyclo[4.2.1]nonane, (I), C 8 H 12 Br 2 O, endo,endo-2,5-bis-(phenylthio)-9-oxabicyclo[4.2.1]nonane, (II), C 20 H 22 OS 2 , and 9,10-dioxatricyclo[4.2.1.1 2,5 ]decane, (III), C 8 H 12 O 2 , were determined and the conformations of these transannular O-heterocyclization products of cycloocta-1,5-diene were defined. The structure determinations reveal a tetrahydrofuran ring having an envelope conformation and an oxepane ring with a twisted-chair conformation in each of (I) and (II), with the two bulky substituents quasi-equatorial or quasi-axial, respectively, both in a trans position in relation to the ring O atom. The tricyclic compound (III) consists of two five-membered envelopes and a 1,4-dioxane chair. The cyclooctane moiety has a twisted-chair conformation in both (I) and (II), whereas it is a chair in (III).

Crystallographic observations of eight-membered ring conformations, retrieved from the Cambridge Structural Database, have been mapped and classified using symmetry-adapted deformation coordinates, principal component analysis and cluster analysis. Seven subsets of eight-membered rings, containing 11–32 conformational observations, have been analysed: cyclooctane (dataset 8C1), cyclooctene (8C2), cycloocta-1,3-diene (8C3), mono-exo-unsaturated carbocycles (8C4), monohetero (8A1), 1,5-dihetero (8A2) and 1,3,5,7-tetrahetero rings (8A3). The energetically preferred (by ~7 kJ mol−1) boat-chair form is adopted by 26 of the 32 examples of 8C1, although varying degrees of twist are induced by fusion to rings of sizes three, four and five. Crystallographic results for other subsets also populate the lower-energy areas of the appropriate potential energy hypersurface, but the analyses are complicated by the effects of ring fusion and by the small numbers of relevant crystal structures in some cases.

In the title compound, C 24 H 33 N 3 O 6 , an end-protected tripeptide, the peptide backbone adopts an incipient 3 10 helical conformation. The peptide units are trans and show significant deviations from planarity. The tripeptide contains an intramolecular 4 → 1 hydrogen bond.

In endo-1,10,11,12,13,13-hexachlorotricyclo[8.2.1.0 2,9 ]-trideca-11-ene, C 13 H 14 Cl 6 , the cyclooctane ring adopts a twist-chair conformation. There is disorder involving the two outermost C atoms of the eight-membered ring in which a conformer having the opposite twist handedness has 15 % population. The near-zero torsion angle of the twist-chair at the ring-fusion bond has a magnitude of 2.3 (4)°. The torsion angles about the bonds comprising the sides of the twist-chair for the major conformer are 81.1 (4) and -51.9 (4)°. The norbomene c=c bond length is 1.331 (4)A

C 1 0H 1 4N 2+ 4 .2Br - cristallise dans C2/c avec a=12.7119, b=6.9016, c=14.6312 A, β=105.755 °; affinement jusqu'a R=0.038. Le cycle central a une conformation chaise.

The title compound, C29H36O10.2C2H6OS, forms a monoclinic crystal containing two hydrogen-bonded dimethyl sulfoxide molecules per 10-deacetyl baccatin III. The lattice is further stabilized by two additional hydrogen bonds and a dipole-dipole interaction. A comparison of 10-deacetyl baccatin III with the structurally similar docetaxel reveals differences primarily in the benzoyl moiety, while comparisons to baccatin III identify relative differences principally in the cyclooctane- and cyclohexane-ring conformations.

The title compound is a minor solid-state photoproduct in the Norrish type II reaction of 1-(4-chlorophenyl)2-cyclooctylethanone. C16H21C10 , Mr= 264.79, triclinic, PI, a=14.335(3), b=15.122(3), c= 15.611 (2),/k, t~ = 76.90 (2), fl= 72.27 (1), 7= 68.00 (1) °, V = 2964 (I) A 3, Z = 8 (four molecules per asymmetric unit), D x = 1. 187 g cm -3, ,;[.(Cu Ka l) = 1.54053/~,/~ = 22.1 cm -~, F(000) = 1136, T= 295 K, R =0.069 for 2958 observed reflections. The four crystallographically independent molecules form a tetrameric hydrogen-bonding pattern. In each of the four molecules the cyclobutanol ring is trans-fused to the cyclooctane ring, and the hydroxyl group is cis to the nearest bridgehead H atom. All four cyclooctane rings exhibit disorder of the outer atoms. On the basis of the above structure, the major photoproduct has been established as the trans-fused-trans-OH isomer. Furthermore, from the known conformation of the reactant, the detailed reaction pathway of the cyclization reaction has been constructed. The pathway involves y-H abstraction by oxygen, followed by rotations about single bonds and angle bending, to allow overlap of radical p-orbitals and formation of a C-C bond. The motions required are minimum for the observed major trans-fused-trans-OH photoproduct, which can be formed in a topochemically controlled reaction.