The title compound, C(13)H(20)O(4)Si(2), is a siloxane-functionalized norbornane anhydride. Both five-membered heterocyclic rings of the mol-ecule have a planar structure, whereas the two five-membered aliphatic rings assume envelope conformations. Weak inter-molecular C-H⋯O hydrogen bonding is present in the crystal structure.

THE TITLE COMPOUND (SYSTEMATIC NAME 3-meth-oxy-24-methyl-9,19-cyclo-lanost-25-ene), C(32)H(54)O, is a triterpenoid which has been isolated from Skimmia laureola. The three six-membered rings adopt chair, slightly distorted half-chair and distorted boat conformations, and the five-membered ring adopts an envelope conformation. All the rings are trans fused.

In the title compound, C(15)H(23)N(3)O(4), the six-membered pyran, cyclo-hexane and trioxane rings adopt chair, chair and boat conformations, respectively, while the seven-membered rings adopt distorted boat and very distorted chair conformations. In the crystal, adjacent mol-ecules are connected by weak C-H⋯N and C-H⋯O inter-actions.

In the title mol-ecule, C(28)H(44)O, the two six-membered rings have a chair conformation and the two five-membered rings haveenvelope conformations. The crystal packing exhibits no short inter-molecular contacts. The absolute configuration was assigned to correspond with that of the known chiral centres in a precursor molecule, which remained unchanged during the synthesis of the title compound.

the 1h and natural-abundance 13c-nmr spectra of 1-thiacyclooctan-3-one (1) have been measured from 25 to -100°c. coalescence is observed in the 1h-nmr spectra of (1) at about -80°c, and attributed to ring inversion in a boat-chair conformation, which is the predominant conformation of (1). the free energy of activation (dg¹) for this process is 9.2±0.2 kcal/mol. the 13c-nmr spectra of (1) is te...

hartree-fock (hf) and density functional theory (dft) methods employed to study the effect of conformational change on the 13c chemical shifts of 6-mono axial and equatorial substituted and 6,7-di axial-axial, equatorial-equatorial and axial-equatorial substitutedderivatives of 5,6,7,8-tetrahydrodibenzo[a,c]cyclo-octene. the geometry of the conformers have been optimized in the gas phase employ...

The title compound, C(23)H(35)BrO(3), synthesized by esterification and bromination of isosteviol, comprises a fused four-ring system. Two of the six-membered rings adopt a regular chair conformation, whereas the remaining six-membered ring is an unsymmetrical distorted chair. The stereochemistry at the two six-membered ring junctions is trans, while the five-membered ring adopts an envelope co...

The title compound, C(27)H(47)NO(3), is a (3-hydroxy-prop-yl)amide derivative of naturally occurring enanti-opure lithocholic acid (3α-hydr-oxy-5β-cholan-24-oic acid). The mol-ecule contains four fused rings: three six-membered rings in chair conformations and one five-membered ring in a half-chair form. The two terminal six-membered rings are cis-fused, while other rings are trans-fused. The s...

In the title compound, C(24)H(36)O(4) [systematic name: (20S)-3β-acet-oxy-16α-hydr-oxy-22,23-bis-nor-5α,17β-cholano(22-16)lac-tone], the three six-membered rings adopt classical chair conformations, while the five-membered rings are in envelope conformations. The ester group attached to ring A is in an equatorial position. Rings A/B, B/C and C/D are trans-fused, whereas rings D/E are cis-fused....

Embedding non-hexagonal rings into sp2-hybridized carbon networks is considered a promising strategy to enrich the family of low-dimensional graphenic structures. However, non-hexagonal rings are energetically unstable compared to the hexagonal counterparts, making it challenging to embed non-hexagonal rings into carbon-based nanostructures in a controllable manner. Here, we report an on-surfac...