In 1961 Wasserman and Frisch identified that interlocked molecules called catenanes (two molecular rings joined like links in a chain) can display non-classical "mechanical" stereochemistry ; when both rings are "oriented" (Cnh symmetry) a catenane exists in two mirror image forms (Figure ). A decade later, Schill proposed that rotaxanes composed of an oriented ring encircling an axle whose ends are distinct are also chiral (Fig. ) . In both cases, the sub-components that make up the interlocked structure are not themselves chiral, which is readily emphasized using commonly employed schematic representations that focus on the symmetry properties of the components (Fig. ). These representations also make clear that such topologically chiral catenanes and mechanically planar chiral rotaxanes are related notionally through ring opening. Although such molecules were initially challenging to make as single enantiomers , recent efforts have allowed them to be accessed in good enantiopurity using standard synthetic approaches .