SYNTHESIS AND ESR OF A NITROXIDE BIRADICAL OF APPROXIMATE D-2H SYMMETRY

A nitroxide biradical ,3,3,5,5,7,7-octamethyldicyclopentano[b;e]pyridi ne (1) and the corresponding monoradical (2-oxy-6-hydroxy) were prepar ed starting from 2,2,5,5-tetramethyl-3-oxopyrrolidine by successive co ndensation with formaldehyde (KOH) or DMF (K in THF), NH4OAc and oxida tion (Na2WO4-H2O2). In ethanol, biradical 1 shows a quintet (\J\ much greater than \a(N)\ = 14.6 G), In frozen ethanol solution, the experim ental spectra (X-band at 120 K and 240 GHz at 7, 15 and 25 K) can be c omputer simulated with the following parameters: D = -64 G; E = 1 G; g (xx) = 2.0093; g(yy) = 2.0064; g(zz) = 2.0020; A(xx) = A(yy) = 8 G; A( zz) = 32.2 G, From the temperature dependence of the high-field spectr a, D is found to be negative.