Although chirality is a whole-molecule property , chemists often trace the appearance of molecular chirality back to one or more rigidly chiral arrangements of atoms in the structure. The most famous of these is the "stereogenic center" embodied by a tetrahedral carbon atom bonded to four different substituents, although stereogenic planes and axes are also found in important natural and synthetic structures. Chiral molecules containing such classical covalent stereogenic units have been studied extensively. Less explored are chiral molecules whose stereochemistry arises absent any covalent stereogenic unit, such as Möbius ladders, 14 molecular knots, and mechanically interlocked molecules8.