3. From rotaxanes to nodes: elements of molecular topology

The spectacular progress made in supramolecular chemistry over the last fifty years has enabled us to develop remarkably efficient strategies for the synthesis of complex molecular objects belonging to the rotaxane, catenane and knot families. Initially regarded as genuine synthetic "curiosities", these molecules have, since the beginning of the twentieth century, raised numerous problems in terms of both their synthesis and their graphical representation in the plane. Catenanes and nodes are all characterized by a so-called "non-trivial" topology. Jean-Pierre Sauvage, winner of the 2016 Nobel Prize in Chemistry for his work in the field of molecular machines, defines chemical topology as "the science of compounds that cannot be represented in a plane without crossing, whatever the deformations to which the molecule is subjected".