ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The radical cation and the radical anion of ‘syn’-cyclobuta[1,2-c:3,4-c′]di-1,6-methano[10]annulene (‘syn’-4a,12a:6a, 10a-bishomobinaphthylene; 3) have been characterized by their hyperfine data. The highly resolved ESR spectrum of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{+ \atop \dot{}} $\end{document} is dominated by a triplet splitting from the outer pair of methano β-protons (Ho). In contrast, the ESR spectrum of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} is poorly resolved with the largest coupling constants arising from perimeter α-protons. The different hyperfine features of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{+ \atop \dot{}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} are rationalized by MO models. The SOMO of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{+ \atop \dot{}} $\end{document} ψSA(b1), has substantial LCAO coefficients of the same sign at the bridged atoms C(1), C(6), C(11), and C(16), whereas in the SOMO of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document}, ψSS(a1), the four atoms lie in the vertical nodal planes. The large width and the reluctance to saturation of the lines in the ESR spectrum of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} are attributed to the near-degeneracy of the lowest antibonding MO's. Due to their similar nodal properties, the SOMO's of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} and the radical anions of binaphthylene (4), 1,6-methano[10]annulene (1), and naphthalene (2) are interrelated. Moreover, because the cyclic π-systems in 3 and 1 deviate in the same way from planarity, the effect of such distortions on the coupling constants, aHμ, of the perimeter α-protons in \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{- \atop \dot{}} $\end{document} should be comparable. Indeed, on going from \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} to \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document}, the |aHμ| values are reduced exactaly by half as much as the corresponding values on passing from \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{- \atop \dot{}} $\end{document} to \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document}, of which the cyclic π-systems are twice contained in \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} respectively.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19930760320
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