If the structure is designed such that the oriented ring is permanently prevented from occupying said mirror plane, the molecule will display fixed molecular chirality (Figure ). This stereogenic unit can be considered to rely on the oriented ring acting as a substituent of the region of C2v ring that it encircles, as in the case of co-conformational-covalent 12 and -mechanical stereochemistry in rotaxanes, 13 effectively lowering the symmetry of the unoriented ring to C1h. We have provisionally termed such molecules as "co-conformationally 'topologically' chiral" to clearly make the link with the conditional topological stereogenic unit of catenanes and emphasize their potentially stereodynamic nature. However, this label is oxymoronic as the stereochemistry of the system is not topologically invariant, hence the quotation marks. ) Chiral and achiral co-conformations of a co-conformationally "topologically" chiral [2]catenane composed of an oriented ring and a C2v ring. (c) A fixed chiral co-conformation of a co-conformationally "topologically" chiral catenane for which co-conformational isomerism is sterically prohibited.