A topologically chiral catenane that is not topologically chiral

Abstract

To consider the topology of a molecule, its structure is reduced to labelled vertices (the atoms) and edges (bonds between them) to generate a molecular graph. If only covalent bonding interactions are included, such graphs are like the structural diagrams commonly employed by chemists atomic geometry is irrelevant; most molecules can be represented as a two-dimensional network and most stereoisomers are topologically identical. In 1960, Wasserman synthesized a molecule in which two rings are held together like in a chain, which is a topological isomer of the separated rings, highlighting that molecules could be topologically non-trivial. This insight has found wider implications in biochemistry but it also led to the assumption that the stereochemistry of catenanes that are chiral due to the orientation of their rings is inherently topological in nature. We show this is incorrect by synthesizing an example whose stereochemistry is Euclidean. Thus, we can unite the stereochemistry of catenanes with that of their topologically trivial cousins, the rotaxanes, paving the way for a more unified approach to their discussion.