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• Chemistry  (2)
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• 1
Electronic Resource
New York, NY : Wiley-Blackwell
Helvetica Chimica Acta 74 (1991), S. 644-653
ISSN: 0018-019X
Keywords: Chemistry ; Organic Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: 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-1H-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.
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• 2
Electronic Resource
New York, NY : Wiley-Blackwell
Helvetica Chimica Acta 73 (1990), S. 2048-2057
ISSN: 0018-019X
Keywords: Chemistry ; Organic Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: 1H- and 13C-chemical shifts of the dianion of dibenzo[a,c]naphthacene (1) have unambiguously been assigned by 2D-NMR spectroscopy. They indicate a remarkable charge distribution, as most of the negative charge is localized on the ‘anthracenic’ moiety, while the ‘phenanthrenic’ moiety is almost neutral. Association of 12- with alkali-metal counterions has only a minor effect on the chemical shifts. The charge partitioning in 12-, which is reproduced by ωβ calculations in the frame of the Hückel model, must, thus, be considered as an intrinsic property of the 4nπ-electron system of 12-. It is rationalized in terms of differing energy contents of the constituent anthracenic and phenanthrenic moieties. ESR and ENDOR studies of the radical anion 1\documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{\relbar}\kern-4pt {.} }}$\end{document} and the radical cation 1\documentclass{article}\pagestyle{empty}\begin{document}$1^{+ \atop \dot{}}$\end{document} show that the π-charge distribution in 12- is reflected by the π-spin distributions in the two radical ions of the alternant hydrocarbon 1.