Linewidth variation in the dinitronitrosomethyl dianion radical in the slow exchange mode

The treatment of nitromethane or dinitromethane in aqueous alkaline solutions (1 to 2·5 M hydroxide) with nitrogen dioxide yields the dianion radical of dinitronitrosomethane [C(NO 2 ) 2 (NO) \documentclass{article}\pagestyle{empty}\begin{document}$ \buildrel\textstyle.\over= $\end{document} ] which at 30° has hfsc of a   N NO   2= 10·75 and 0·65 and a N NO = 5·80 g. Restricted rotation about the CNO bond causes magnetic non‐equivalence of the two nitro groups which can slowly exchange giving rise to line broadening. The use of 15 N labeled nitrogen dioxide gave the dianion radical\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm [C(}^{{\rm 15}} {\rm NO}_{\rm 2} {\rm)(}^{{\rm 14}} {\rm NO}_{\rm 2} {\rm)(}^{{\rm 15}} {\rm NO)} \buildrel\textstyle.\over= {\rm]} $$\end{document}which exists in two equally populated conformations, each of which shows the expected line broadening for a ‘slow exchange’ process in which the nitro groups are being interconverted.