ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The radical anion of [2.2]metaparacyclophane-1,9-diene (1) has been fully characterized by its hyperfine data with the use of ESR, ENDOR, and TRIPLE-resonance spectroscopy. Assignments of all proton-coupling constants are based on comparison with the spectra of the radical anions of the 8-deuterio-, 1,2,9,10-tetradeuterio-, and 1,10,12,13,15,16-hexadeuterio derivative. The spin distribution in 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} drastically differs from that in the radical anion of [2.2]metaparacyclophane (4), and it is not readily interpreted by semi-empirical MO-methods. The radical anions of 8-fluoro- (2) and 8-cyano[2.2]metaparacyclophane-1,9-diene (3) have also been investigated. Substitution of 1 by an F-atom in the ‘exposed’ 8-position, to yield 2, has only a minor effect on the π-spin distribution in the radical anion, as evidenced by the similar proton-hyperfine data for 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} and 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}. The 19F-coupling constant for 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} is much smaller than expected, thus indicating a pronounced ‘ortho-effect’ in the pertinent position. The ESR and ENDOR spectra of 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} in 1,2-dimethoxyethane (counterion K+) reveal an equilibrium between a tightly and a loosely ion-paired radical anion. Whereas the former is present exclusively in 2-methyltetrahydrofuran (K+), the latter prevails in N,N-dimethylformamide (Et4N+) and in mixtures of 1,2-dimethoxyethane with N,N′,N,N″,N,′N″-hexamethylphosphoric triamide (K+). The high temperatures required for the conformational flipping of the meta-bridged benzene ring in 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}, 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}, and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} to be fast on the hyperfine time-scale are well above the range appropriate for the studies of these radical anions.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19900730726
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