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Effects of Non‐planarity in the Radical Anions of Tribenzo[ a , c , e ]cyclooctenes
Author(s) -
Felder Patrick,
Gerson Fabian,
Gescheidt Georg,
Heckendorn René,
Tong TatHung,
Wang XiaoMin,
Wong Henry N. C.,
Hou XueLong
Publication year - 1991
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19910740321
Subject(s) - chemistry , planarity testing , steric effects , fluorene , ring (chemistry) , cyclic voltammetry , crystallography , derivative (finance) , medicinal chemistry , photochemistry , stereochemistry , organic chemistry , electrochemistry , electrode , polymer , financial economics , economics
Reduction of tribenzo[ a , c , e ]cyclooctene ( 2 ) and its 2,3‐ and 1,4‐dimethyl derivatives ( 4 and 5 ), as well as of 1,1‐dimethyl‐10,11‐propane‐2,2‐diylidene‐1 H ‐benzo[5,6]cycloocta[1,2,3,4‐ def ]fluorene ( 6 ) and its 5,6‐didehydro derivative ( 7 ) was followed by cyclic voltammetry. The radical anions of these compounds and those of their derivatives (D) 2 , (D) 5 , and (D) 6 , deuteratsd at C(9) in 1 and 5 or in the corresponding position of 6, have been characterized with the use of ESR, ENDOR, and TRIPLE‐resonance spectroscopy. The cyclic‐voltammetric and proton‐hyperfine data are consistent with the increasing deviations of the radical anions from planarity in the order These deviations, due to steric or interferences in the peri ‐positions 1↔14 and 4↔5, are removed in and by the introduction of bridging groups. The non‐plalarity affects the thermodynamic and kinetic stabilities of the radical anions and causes a shift in the π‐spin distribution away from that benzene ring which is linked to the two others by the essential single bonds C(4a)C(4b) and C(14a)C(14b). This finding suggests that the steric hindrance in , and is alleviated by twisting this ring out of coplanarity with the remaining ( Z )‐stilbene‐like π‐system.