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Möbius aromaticity in small [ n ] trans ‐annulenes?
Author(s) -
Havenith Remco W. A.,
van Lenthe Joop H.,
Jenneskens Leonardus W.
Publication year - 2001
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.1089
Subject(s) - annulene , antiaromaticity , aromaticity , chemistry , ab initio , computational chemistry , cyclooctatetraene , benzene , atomic orbital , character (mathematics) , electron , quantum mechanics , physics , molecule , mathematics , organic chemistry , geometry
It is shown that the approximations for the derivation of the Hückel–Möbius rules used in (semi‐)empirical studies cannot be maintained at the ab initio level of theory. As the orbital degeneracy, obtained using the Hückel approximations, is not maintained at the ab initio level, the [4 n +2] and [4 n ] Hückel–Möbius rules do not apply exactly. The existence of possible Möbius character for cis , cis , trans ‐cyclohexatriene ( trans ‐benzene, 2 ) and cis, cis, cis, trans ‐cyclooctatetraene ( trans ‐ 4 ) is investigated; their structural and magnetic properties show that both compounds possess neither antiaromatic nor aromatic properties, respectively. The lack of cyclic π‐electron conjugation is due to the reduced overlap between the p π ‐orbitals. This is demonstrated for trans ‐ 4 in which the trans double bond is forced into the geometry of that of the cyclononatetraenyl cation ( 6 ). In that case, trans ‐ 4 possesses aromatic properties (NICS −12.9 ppm). © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 85: 52–60, 2001