Which π-Clamped Conjugated Monocycles Exhibit Ring Currents?

Quenching/survival of ring currents in π-clamped conjugated monocycles is controlled by the match or mismatch in parity between the frontier orbitals of the central π-conjugated 4n+2/4n monocycle and those of the clamps. Changes in ring current are not primarily caused by bond alternation or ‘Mills–Nixon’ effects; current and geometry changes on clamping are both consequences of electronic structure.