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Effects of Non-planarity in the Radical Anions of Tribenzo[a,c,e]cyclooctenes

✍ Scribed by Patrick Felder; Fabian Gerson; Georg Gescheidt; René Heckendorn; Tat-Hung Tong; Xiao-Min Wang; Henry N. C. Wong; Xue-Long Hou

Publisher
John Wiley and Sons
Year
1991
Tongue
German
Weight
448 KB
Volume
74
Category
Article
ISSN
0018-019X

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✦ Synopsis

Dedicated to Prof. Edgar Heilhronner on the occasion of his 70th birthday (4.11.91) Reduction of tribenzo[a,c,e]cyclooctene (2) and its 2,3-and 1,4-dimethyl derivatives (4 and 5 ) , as well as of l,l-dimethyl-l0,11-propane-2,2-diylidene-lH-benzo[5,6]cycloocta[ 1,2,3,4-deflfluorene (6) and its 5,6didehydro 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, deuterated at C(9) in 2 and 5 or in the corresponding position of 6, have been characterized with the use of ESR, ENDOR, and TRIPLE-resonance spectroscopy. The cyclic-voltammetic and proton-hyperfine data are consistent with the increasing deviations of the radical anions from planarity in the order 6:, 7: < 2:, 4: < 5:. These deviations, due to steric H t t H (27, 4:) or H-Me (5:) interferences in theperipositions 1-14 and 4-5, are removed in 6' and 7' by the introduction of bridging groups. The non-planarity affects the thermodynamic and kinetic stabilities of the radical anions and causes a shift in the m p i n 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 2:, 4:, and 5: is alleviated by twisting this ring out of coplanarity with the remaining (a-stilbene-like mystem.

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