The Radical Anion of 1,2-Diphenylcyclopentene

✍ Scribed by Fabian Gerson; William B. Martin Jr.; Christoph Wydler

• Publisher: John Wiley and Sons
• Year: 1979
• Tongue: German
• Weight: 433 KB
• Volume: 62
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19790620802

✦ Synopsis

Abstract

ESR. and ENDOR. studies are reported for the radical anions of 1,2‐diphenylcyclopentene (3) and its di(pe+deuteriophenyl)‐derivative (3‐D~10~). Comparison of the coupling constants of the phenyl protons in 3\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}. with the analogous values for the radical anions of 1,2‐diphenyl substituted cyclopropene (1) and cyclobutene (2) reveals regular changes in the sequence 1\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, 2\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, 3\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}, which are caused by an increasing twist of the phenyl groups about the C(1), C(1′)‐ and C(2), C(1″)‐bonds linking them to the ethylene fragment. Such a twist is shown to be also responsible for the large difference in the coupling constants of the methylene β‐protons in 3\documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document}. (0.659 and 0.293 mT). It is suggested that ‐ in order to minimize the losses caused by this twist in the π‐delocalization energy ‐ the 2 p~z~‐axes at the centres 1 and 2 deviate from a perpendicular orientation to the mean plane of the cyclopentene ring. A deviation by 19° from such an orientation is required to account for the observed β‐proton coupling constants in terms of their conventional cos^2^‐dependence on the dihedral angles θ.