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The oxidation of N-[(4-nitrophenyl)thio]-2-t-butyl-1-aminopyrene yielded a quite persistent and oxygen-insensitive N-[(4-nitrophenyl)thio]-2-t-butyl-1-pyrenylaminy radical (3), which was isolated as reddish-black fine needles. The hyperfine coupling (hfc) constants for the aminyl were determined by ESR and 1H ENDOR measurements, indicating that there is an extensive delocalization of the unpaired electron from the nitrogen onto the pyrene ring. A comparison of the hfc constants with structurally close N-[(4-nitrophenyl)thio]-7-t-butyl-1-pyrenylaminyl (1) and N-[(4-nitrophenyl)thio]-2,7-di-t-butyl-1-pyrenylaminyl (2) showed that although the spin-density distribution of 3 is similar to that of 2, it is greatly different from that of 1. Magnetic susceptibility measurements of 3 in solid radical crystals showed that the magnetic interaction between the radical spins is strongly antiferromagnetic, giving J/k = −108 and −192 K for 2 and 3, respectively.

N-(Arylthio)-7-tert-butyl-1-pyrenylaminyl (2) and N-[(4-nitrophenyl)- thio]-2,7-di-tert-butyl-1-pyrenylaminyl radicals (3) are prepared by PbO 2 oxidation of N-(arylthio)-7-tert-butyl-1-aminopyrenes and N-[(4- nitrophenyl)thio]-2,7-di-tert-butyl-1-aminopyrene, respectively, and studied by ESR and ENDOR spectroscopy. The kinetic ESR study shows that, while aminyls (2) gradually decompose in solution at room temperature, aminyl (3) is quite persistent, even in refluxing benzene, and shows no tendency to dimerize, even at low temperatures. These interesting pro- perties of (3) permit us to isolate (3) as radical crystals in 28-31% yield. The hyperfine splitting (hfs) constants of (2) and (3), determi- ned by ESR and ENDOR spectroscopic methods, show an extensive delocali- zation of the unpaired electron onto the pyrene ring

Oxidation of 2,7-di-t-butyl-1-hydroxypyrene yields persistent and oxygen-insensitive 2,7-di-t-butyl-1-pyrenoxy radical (2) with the following ESR parameters: (aH) 0.532, 0.449, 0.430, 0.389, 0.164, 0.110, and 0.095 mT (aH), and 2.0037 (g). Radical 2 is isolated as a diamagnetic dimer which, upon dissolution, dissociates into 2 at room temperature. The ΔH and ΔS values for the dimer−1 and −35 ± 15 J mol−1 K−1, respectively. The negative ΔS value is briefly discussed.2 radical equilibrium are determined to be 7.2 ± 2.0 kJ mol

Oxidation of N-[(4-nitrophenyl)thio]-2,7-di-t-butyl-1-aminopyrene yields an exceptionally persistent and oxygen-insensitive N-[(4-nitrophenyl)thio]-2,7-di-t-butyl-1-pyrenylaminyl, which has been isolated as pure radical crystals in 31% yield. The crystals can be stored, without decomposition, for a long period.

Oxidation of 2,7-di-tert-butyl-1-hydroxypyrene 1 yields the exceptionally persistent and oxygen-insensitive 2,7-di-tert-butylpyren-1-oxyl radical 2 whose EPR and ENDOR spectra give the following proton hyperfine coupling (hfc) constants: 0.526, 0.445, 0.426, 0.386, 0.157, 0.107, 0.088 and 0.0054 mT (g= 2.0037). The assignments of the protons are accomplished by measuring the EPR and ENDOR spectra of partly deuteriated 2,7-di-tert-butyl(4,5,9,10-2H4)pyren-1-oxyl radical. Radical 2 is isolated as a dimer which is in equilibrium with 2 in solution, even at low temperatures. The thermodynamic parameters for the equilibrium are determined to be 7.2 ± 2.0 kJ mol–1(ΔH) and –35 ± 15 J mol–1 K–1(ΔS), respectively. The very low ΔH and negative ΔS values are briefly discussed.