Residual topological isomerism of intertwined molecules.

The growing number of molecular assemblies with unusual geometry and topology requires from time to time a revision of certain aspects of stereochemistry. The present paper analyzes several representatives of intertwined molecules that have bridges connecting their loops. In spite of the experimentally proven chirality, these species lack elements of both classical and topological chirality. Due to the relationship of these types of molecules to the well-recognized topologically nontrivial compounds, such as catenanes and knots, we propose the term "residual topology" illustrated by a simple scheme of excessive or missing bridges that could be excluded or included, respectively, in molecular graphs of these species to render them topologically nontrivial. This concept paper represents, therefore, an update on the currently applied nomenclature.