Conformational enantiomeric

On the other hand, twistane is a chiral molecule and the disconnection of either one of the two identical strategic bonds, 11 and 12, in each one of two possible enantiomers leads to one of the two possible conformationally enantiomeric cis-decalins (Aj and A2), the resolution of which is indeed not possible since they... 

The absence of an achiral boundary along the conformational enantiomerization trajectory of chemically achiral compounds, such as the ones discussed above, precludes partitioning of conformations along the path into homochirality classes. As noted above, under such circumstances it becomes meaningless to speak of these conformations as right-handed or left-handed because no point can be defined, other than arbitrarily, where right switches to left and vice versa. 

Conformational enantiomerism. trans-Cyclooctene is strained, unable to achieve a symmetric planar conformation. It is locked into one of these two enantiomeric conformations. Either pure enantiomer is optically active, with [a] = 430°. 

Even a simple strained molecule can show conformational enantiomerism. trans-Cyclooctene is the smallest stable trans-cycloalkene, and it is strained. If trans-cyclooctene existed as a planar ring, even for an instant, it could not be chiral. Make a molecular model of trans-cyclooctene, however, and you will see that it cannot exist as a planar ring. Its ring is folded into the three-dimensional structure pictured in Figure 5-18. The mirror image of this structure is different, and trans-cyclooctene is a chiral molecule. In fact, the enantiomers of iran.v-cyclooclcnc have been separated and characterized, and they are optically active. 

Kano, K., Tsujino, N., Kim, M. (1992). Mechanisms for steroid-induced conformational enantiomerism of bilirubin in protic solvents, J. Chem. Soc., Perkin Trans. 2, p. 

Conformational enantiomers based on the torsional twist about the Cp(centroid)-Fe-Cp(centroid) axis are possible in the case of the l,l -di-substituted ferrocene, as shown in Fig. 1 [13,64]. Conformational enantiomers can interconvert with ease due to the low barrier of Cp ring twisting. The introduction of peptide chains into a ferrocene scaffold is envisaged to induce conformational enantiomerization by restriction of the torsional twist through intramolecular interchain hydrogen bonding. 

Armed with this knowledge, the reason for the low ees observed in salts that exhibit conformational enantiomerism is straightforward half of the molecules in the crystal react to give one photoproduct enantiomer while the other half react to form its optical antipode. The reason the ee is not zero is that the conformational enantiomers are in fact independent molecules that reside in structurally different... 

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