The ESR. Spectrum of the Diphenylcyclopropenone Radical Anion

Abstract

Abstract The ESR. spectrum of the relatively unstable radical anion of diphenylcyclo‐propenone (II) has been observed upon electrolytic reduction of II in N , N ‐di‐methylformamide and 1,2‐dimethoxyethane. Simple MO models account well for the π‐spin distribution and for the restricted rotation of the phenyl substituents in II \documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document} . A rather facile loss of a CO molecule by II \documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document} results in formation of the radical anion of tolane (diphenylacetylene; III). No ESR. spectra could be obtained for the radical anions of dialkylcyclopropenones which are even shorter‐lived than II \documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document} , although decay by decarbonylation seems to be less favoured with them than with II \documentclass{article}\pagestyle{empty}\begin{document}$ ^{\ominus \atop \dot{}} $\end{document} . In presence of air, electrolytic reduction of either II or its dimethyl and di‐ t ‐butyl analogues yields the correspondingly disubstituted semidione anions.