Investigation of a Putative Möbius Aromatic Hydrocarbon. The Effect of Benzannelation on Möbius [4n]Annulene Aromaticity
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- 作者：Claire Castro ; Zhongfang Chen ; Chaitanya S. Wannere ; Haijun Jiao ; William L. Karney ; Michael Mauksch ; Ralph Puchta ; Nico J. R. van Eikema Hommes ; and Paul von Ragué ; Schleyer
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：March 2, 2005
- 年：2005
- 卷：127
- 期：8
- 页码：2425 - 2432
- 全文大小：509K
- 年卷期：v.127,no.8(March 2, 2005)
- ISSN：1520-5126
文摘
The first experimental example of a [4n]annulene derivative with one Möbius twist, 1, wassynthesized recently [Ajami, D.; Oeckler, O.; Simon, A.; Herges, R. Nature 2003, 426, 819] and waspurported to possess aromatic character. However, critical analysis of the published crystallographic dataindicates that the Möbius [16]annulene core of 1 shows large bond alternation (
r up to 0.157 Å).Delocalization in this core is inhibited by large dihedral angles, which hinders effective 
overlap. Thisconclusion is supported by computational results (B3LYP/6-311+G**) on 1 and several less benzannelatedderivatives, based on geometric (r, rm, Julg A, HOMA) and magnetic (NICS, magnetic susceptibilityexaltation) criteria of aromaticity. That benzannelation results in bond localization in the [16]annulene coreis shown by additional computations on benzannelated derivatives of other Möbius aromatic species.Additionally, the aromatic stabilization energy (ASE) of 1 has been reinvestigated using two differentprocedures. Evaluation of uncorrected ISEII values of just the polyene bridge portion of 1 and its Hückelcounterpart suggests that stabilization of 1 relative to its Hückel isomer is confined to the polyene bridgeand is not due to a delocalized circuit. Furthermore, application of s-cis/s-trans corrections lowers theISEII value of 1 from 4.0 kcal/mol to 0.6 kcal/mol, suggesting that 1 is nonaromatic.
r up to 0.157 Å).Delocalization in this core is inhibited by large dihedral angles, which hinders effective overlap. Thisconclusion is supported by computational results (B3LYP/6-311+G**) on 1 and several less benzannelatedderivatives, based on geometric (r, rm, Julg A, HOMA) and magnetic (NICS, magnetic susceptibilityexaltation) criteria of aromaticity. That benzannelation results in bond localization in the [16]annulene coreis shown by additional computations on benzannelated derivatives of other Möbius aromatic species.Additionally, the aromatic stabilization energy (ASE) of 1 has been reinvestigated using two differentprocedures. Evaluation of uncorrected ISEII values of just the polyene bridge portion of 1 and its Hückelcounterpart suggests that stabilization of 1 relative to its Hückel isomer is confined to the polyene bridgeand is not due to a delocalized circuit. Furthermore, application of s-cis/s-trans corrections lowers theISEII value of 1 from 4.0 kcal/mol to 0.6 kcal/mol, suggesting that 1 is nonaromatic.