Lemniscular hexaphyrins as examples of aromatic and antiaromatic double-twist Mobius molecules

Two reported [26] and [28]hexaphyrins are analyzed via measured and computed geometries and NMR-shieldings as examples of respectively 4n + 2 pi-electron aromatic and 4n pi-electron antiaromatic double-twist Mobius ring systems, adopting a lemniscular/figure-eight topology with linking number L-K = 2 pi. Values of local twist (T-w) and nonlocal writhe (W-R) derived from the relation L-k = T-w + W-R appear relatively insensitive to the aromatic/antiaromatic character. The [26]hexaphyrin may adopt differing solution and solid-state conformations.