Applications of ENDOR spectroscopy to radical cations in freon matrices. Part 2 . The radical cation of 2,3‐diazabicyclo[2.2.2]oct‐2‐ene

The radical cation of 2,3‐diazabicyclo[2.2.2]oct‐2‐ene (1) , generated by γ‐rays in a CF 2 ClCFCl 2 matrix, has been fully characterized by its hyperfine data with the use of ESR, ENDOR, and TRIPLE resonance spectroscopy. The isotropic coupling constants for \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }}$\end{document} are +3.14 mT for the two 14 N Nuclei in the azo group, −0.336 mT for the two protons at the bridgehead C atoms, and +151 and +0.135 mT for the sets of four exo ‐ and four endo ‐protons, respectively. MO calculations indicate that these values are consistent with an electron removal from an orbital represented by the antibonding combination (n_) of the lone‐pair atomic orbitals at the two N atoms. The corresponding radical anion \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }}$\end{document} is persistent in fluid solution and its hyperfine data, combined with MO calculations, point to an electron uptake into the antibonding π orbital (π*) of the azo group. It is, thus, reasonable to classify \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{+}\kern-4pt {.} }}$\end{document} as a σ and \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }}$\end{document} as a π radical.