Atropisomerism in a belt-persistent nanohoop molecule: rotational restriction forced by macrocyclic ring strain.

Enough strain! Strain in a macrocyclic ring hinders the rotation of an arylene panel in a nanohoop molecule containing four chrysenylene units (see picture). Unlike conventional rotational restrictions in biaryl systems, the new atropisomerism does not require any steric hinderance from the substituents. The study of atropisomerism also provides the first experimental insights into the relative stability of nanohoop structures.