Möbius aromaticity

A monocyclic array of orbitals in which there is a single out-of-phase overlap (or, more generally, an odd number of out-of-phase overlaps) reveals the opposite pattern of aromatic character to Hückel systems; with electrons it is stabilized (aromatic), whereas with it is destabilized (antiaromatic). In the excited state Möbius π-electron systems are stabilized, and systems are destabilized. No examples of ground-state Möbius π-electron systems are known, but the concept has been applied to transition states of pericyclic reactions [See: aromatic]. The name is derived from the topological analogy of such an arrangement of orbitals to a Möbius strip.