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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 4 n electrons it is stabilized (aromatic), whereas with 4 n + 2 it is destabilized (antiaromatic). In the excited state 4 n + 2 Möbius π-electron systems are stabilized, and 4 n 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.
See also: Hückel 4 n + 2 rule
Source:
PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1141
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IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook.
Last update: 2014-02-24; version: 2.3.3.
DOI of this term: doi:10.1351/goldbook.M03957.
Original PDF version: http://www.iupac.org/goldbook/M03957.pdf. The PDF version is out of date and is provided for reference purposes only. For some entries, the PDF version may be unavailable.
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