Aromaticity in Semi‐Condensed Figure‐Eight Molecules

Abstract

AbstractElectron delocalization and aromaticity was comparatively evaluated in recently synthesized figure‐eight molecules made of two condensed U‐shaped polycyclic aromatic hydrocarbon moieties connected either by two single bonds or by two para‐phenylene groups. The selected examples include molecules that incorporate eight‐membered and sixteen‐membered rings, as well as a doubly [5]helicene‐bridged (1,4)cyclophane. We probe whether some electron delocalization could occur through the stereogenic single bonds in these molecules: Is aromaticity purely (semi‐)local, or possibly also global in these molecules? It was concluded that the situation can go from a purely (semi‐)local character when the dihedral angle at the connecting single bonds is large, such as in biphenyl, to a predominantly (semi‐)local character with a minor global contribution when the dihedral angle is small, such as in the para‐phenylene connectors of the [5] helicene‐bridged cyclophane.