The Radical Cation of Azatriquinane: An ESR Study

Azatriquinane (= 10-azatricyclo[5.2.1.0^1,10]decane; 1) was oxidized to its radical cation 1^·+ by γ- irradiation in a CF₂ClCFCl₂ matrix at 77 K. A prominent feature of the ESR spectrum of 1^·+ is the ¹⁴N-hyperfine anisotropy which broadens the components with M₁(¹⁴N)=±1. The observed coupling constants are a_N=+2.5 and a_H = + 4.0 mT for the ¹⁴N nucleus and the three methine β-protons, respectively. While the a_N value points to pyramidalization at the N-atom comparable to that in the radical cation of quinuclidine (= 1-azabicyclo[2.2.2]octane; 4), an eclipsing of the singly occupied orbital at this atom by the three C-H_β bonds is indicated in view of the large a_H value. Theoretical calculations on the geometry of 1^·+ are in accord with the conclusions drawn from the experimental findings.