Premium
The Radical Anions of 1,2‐diphenylcyclohexene and Structurally Related Compounds. Conformational ESR and ENDOR studies
Author(s) -
Gerson Fabian,
Martin Williiam B.
Publication year - 1987
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19870700614
Subject(s) - chemistry , hyperfine structure , cyclohexene , ring (chemistry) , stereochemistry , crystallography , nuclear magnetic resonance , atomic physics , physics , organic chemistry , catalysis
ESR, ENDOR, and TRIPLE resonance studies have been performed on the radical anions of 1,2‐diphenylcyclohex‐1‐ene ( 4 ), 1,2‐di(perdeuteriophenyl)cyclohex‐1‐ene ((D 10 ) 4 ) the trans ‐configurated 3,4‐diphenyl‐8‐oxabicyclo[4.3.0]non‐3‐ene ( 5 ) and its 2,2,5,5‐tetradeuterio derivative (D 4 ) 5 , and 2,3‐diphenyl‐8,9,10‐trinorborn‐2‐ene ( 6 ). The spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} exhibit strong temperature dependence along with a specific broadening of ESR hyperfine lines and proton ENDOR signals. The coupling constant, which bears the main responsibility for these features, is that of the β‐protons in the quasi ‐equatorial positions of the cyclohexene ring, and the experimental findings are readily rationlized in terms of relatively modest conformational changes without invoking the inversion of the half‐chair form. The hyperfine data for the β‐protons in \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} closely resemble the corresponding low‐temperature values for \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} , However, the ‘unusual’ features observed for \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} are absent in the ESR and ENDOR spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} , because the half‐chair conformation of the cyclohexene ring in \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} is deprived of its flexibility. Although the boat form of this ring in \documentclass{article}\pagestyle{empty}\begin{document}$ 6^{- \atop \dot{}} $\end{document} is also rigid, the spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ 6^{- \atop \dot{}} $\end{document} are temperature‐dependent, due to an interconversion between two propeller‐like conformations of the phenyl groups. The pertinent barrier is 30 ± 5 kJ ·mol −1 . An analogous interconversion presumably takes place in \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 5^{- \atop \dot{}} $\end{document} as well, but, unlike \documentclass{article}\pagestyle{empty}\begin{document}$ 6^{- \atop \dot{}} $\end{document} , it is not amenable to experimental study.