Appendix A. Naming and numbering scheme for cyclooctane conformers.

A.1. Boat-chair family.

We have tried to keep the scheme simple and, primarily, to make it easy to draw a particular conformer from the name. BC has a C_s point group. In general, as soon as substituents are introduced in the ring, the point group becomes C₁ unless the substituents happen to lie in the carbons split by the mirror plane that defines C_s symmetry. Thus, in the general case, we can distinguish two enantiomeric BC conformers, one \ ``left-oriented'' and one ``right-oriented''

Figure A.1. ``Left-oriented'' and ``right-oriented'' BCs[fig.chiralBCs.gif, 1.640KB]

We denote the ``left-oriented'' version by BC, while the ``right-oriented'' is BC'. The numbers on the carbons follow a specular relationship to the numbers in the conformational enantiomer.

To name a particular conformer, we keep the numbering fixed. We do follow the chemical convention of always trying to assign the lowest possible numbers, within the constraint that the positions of fixed number positions. Thus, if the substitution pattern allows it, the choice between BC and BC' depends on which one yields the lowest numbers. We define completely the position of a substituent by choosing the appropriate letter among the following:

e

equatorial

a

axial

b

bowsprit

f

flagpole

i

isoclinal

Figure A.2. Labels for the orientations of substituents in BC[fig.BCtags.gif, 0.939KB]

The point group of TBC is C₂. This is a disymmetric group and allows for chiral shapes. We can therefore distinguish two conformers, one ``twisted to the right'' and one ``twisted to the left''. We designate the one ``twisted to the left'' as TBC, and the ``twisted to the right'' as TBC'. See the scheme:

Figure A.3. ``Left-oriented'' and ``right-oriented'' TBCs[fig.chiralTBCs.gif, 1.689KB]

The labels for the orientation are as follows:

Figure A.4. Labels for the orientations of substituents in TBC[fig.TBCtags.gif, 1.257KB]

A.2. Chair-chair family.

The CC has a C_2v point group. Its shape is slightly elliptical (when seen from the z axis). It has four sets of isochronous carbons (same NMR signal by symmetry). C_2v is not a chiral point group so we only have:

Figure A.5. CC numbering and labeling scheme.[fig.CCtags.gif, 0.846KB]

The numbering starts on one carbon along the major axis of the ellipse.

The Crown is a very high-symmetry conformer, with a D_4d point group. All the carbons are undistinguishable by symmetry operations so the choice of any particular carbon to start the numbering is immaterial. The Crown is actually a special case of the CC , but we give the numbering and labels for substituents for the sake of completeness. The introduction of substituents is bound to perturb the high symmetry of the molecule, rendering it as a CC. We do not have any examples of crowns in our results, and we do not find any crown conformers among substituted cyclooctanes, although some authors have referred to CCs as crowns in the past.

Figure A.6. Crown.[fig.crowntags.gif, 0.941KB]

The TCC has a D₂ point group. This is a disymmetric group, so we find two enantiomers. The numbering and the names follow this scheme:

Figure A.7. TCC numbering and labeling scheme.[fig.TCCtags.gif, 1.751KB]

The TC has a C_2h point group. The numbering and the names follow this scheme:

Figure A.8. TC numbering and labeling scheme.[fig.TCtags.gif, 1.593KB]

The C has a C_2h point group. The numbering and labeling are as follows:

Figure A.9. C numbering and labeling scheme.[fig.Ctags.gif, 0.971KB]

A.3. Boat-boat family.

Boat.

Figure A.10. B numbering and labeling scheme.[fig.Btags.gif, 0.944KB]

Boat-boat.

Figure A.11. BB numbering and labeling scheme.[fig.BBtags.gif, 0.997KB]

Twist-boat.

Figure A.12. TB numbering and labeling scheme.[fig.TBtags.gif, 1.700KB]