Segregation of Charge in Ions of Dibenzo[ a , c ]naphthacene: Relation of Topology and Electronic Structure. An NMR, ESR, and ENDOR Study

1 H‐ and 13 C‐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 1 2− with alkali‐metal counterions has only a minor effect on the chemical shifts. The charge partitioning in 1 2− , which is reproduced by ωβ calculations in the frame of the Hückel model, must, thus, be considered as an intrinsic property of the 4 n π‐electron system of 1 2− . 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 1 2− is reflected by the π‐spin distributions in the two radical ions of the alternant hydrocarbon 1 .