Geometry-controlled reactivity and dynamics in organic molecules

It is well established that strain in organic molecules is linked to having nonideal bond lengths, bond angles and unfavourable non-covalent interactions. The constrained geometries of ring systems are particularly predisposed to creating strain. Recently, there has been increased interest in leveraging this property of rings as a synthetic tool by building strain into substrates to activate a desired bond-cleavage step. However, one could also envisage alternative uses of strain. Here we outline how geometry control can be exploited to ‘switch on’ dynamic processes or stabilize reactive transition states. By designing constrained molecular structures that direct strain on particular bonds or functional groups, transformations that are otherwise energetically uphill can become favoured. This phenomenon can subvert our expectations about the reactivity and properties of organic molecules, giving rise to unusual bonding modes.