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 to describe molecules, except that in topological terms, atomic geometry is largely irrelevant; most molecules can be represented as a two-dimensional network and most covalent stereogenic units are topologically irrelevant. 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 components, leading to the realization that molecules could be topologically non-trivial. This insight found wider implications in biochemistry and materials science but also led to the assumption that the stereochemistry of chiral catenanes is inherently topological in nature. We show this is incorrect by synthesizing an example whose stereogenic unit is identical to previous reports but 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 unified approach to their discussion.