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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.