Insights from semi-structural schematic representations. The minimal schematic representation of a mechanically axially chiral catenane (Fig. ) does not specify how the facial dissymmetry of the macrocycles arises. The most obvious way this can be achieved chemically is by including a prochiral unit in both rings (I, Fig. ) 9,29, . Strikingly, whereas the minimal schematic representation of a mechanically axially chiral catenane suggests there can be no rotaxane equivalent of this stereogenic unit (Fig. ), the semi-structural representation reveals that the notional ring opening process gives rise to a chiral rotaxane (Fig. ); even when the ring encircles the prochiral unit of the axle (IV) there is no representation that is achiral. Thus, we see that rotaxanes can display a previously unremarked upon noncanonical mechanically axially chiral stereogenic (Supplementary section 12.1) unit that displays similar co-conformational diastereoisomerism (V).