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Radical Anions of Some Dehydro[ n ]annulene‐diones with n = 16 and 18
Author(s) -
Gerson Fabian,
Beckhaus HansDieter,
Sondheimer Franz
Publication year - 1980
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198000078
Subject(s) - chemistry , annulene , intramolecular force , antiaromaticity , counterion , aromaticity , hyperfine structure , ion , radical ion , computational chemistry , crystallography , stereochemistry , molecule , organic chemistry , physics , quantum mechanics
Radical anions of 10,15‐dimethyl‐2,4,11,13‐tetrakisdehydro[18]annulene‐1,6‐dione (syn‐ 18 ), 6,15‐dimethyl‐2,4,11,13‐tetrakisdehydro[18]annulene‐1,10‐dione (anti‐ 18 ) and 8,13‐dimethyl‐2,9,11‐trisdehydro[16]annulene‐1,4‐dione (syn‐ 16 ) have been investigated by ESR and, in part, by ENDOR spectroscopy. The hyperfine patterns of these radical anions depend on the rate of intramolecular interconversion between two equivalent ion pairs in which the counterion is associated with one oxygen atom. It is found that the polarity of the solvent, which is an important factor influencing such a rate, does not affect the spectra of syn‐16 ⊕ . quite in the same way as those of syn‐18 ⊕ . and anti‐16 ⊕ . This behavior, together with the lower stability of the former radical anion as compared to the two latter ones, points to substantial differences in physico‐chemical properties. Simple MO models indicate that the electronic structures of syn‐16 ⊕ ., syn‐18 ⊕ . and anti‐16 ⊕ . can be related to those of the corresponding 16π‐ and 18π‐perimeters. One is thus tempted to interpret the observed differences in terms of Hückel's rule of “aromaticity” and “antiaromaticity”.