The anion radical of azobispyridin N ‐oxide

The anion radical of the fully aromatic di‐ N ‐oxide system of azobispyridine N ‐oxide was prepared and studied by ESR. Utilising computer simulation and CNDO computation the ESR spectrum was interpreted as follows:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm a}_{\rm N}^{{\rm N} = {\rm N}} = 6 \cdot 93{\rm G};\quad{\rm a}_{\rm N}^{{\rm N} - 0} = 3 \cdot 95{\rm G};\quad{\rm a}_{{\rm H} - 3,5}^{{\rm CH}} = 1 \cdot 92{\rm G};} \\ {{\rm a}_{{\rm H} - 2,6}^{{\rm CH}} = 0 \cdot 61{\rm G}.} \\ \end{array} $$\end{document}Using appropriate equations the spin densities were calculated at\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} \begin{array}{l}\\ \rho _{\rm N}^{{\rm N} = {\rm N}} = 0 \cdot 214;{\rm }\quad\rho _{\rm N}^{{\rm N} - {\rm 0}} = 0 \cdot 148;{\rm }\quad\rho _{{\rm C} - 3,5} = 0 \cdot 00800; \\ \end{array} \\ {\rho _{{\rm C} - 2,6} = 0 \cdot 0254.} \\ \end{array} $$\end{document}Ths semi‐quinoidal nature of the radical suggests a possible use as a spin label.