Direct detection of the radical cation of 2,6-di-tert-butyl-4-methylphenol generated by electron-transfer oxidation with matrix alkyl halide cation radicals. A low-temperature EPR and UV-VIS optical absorption study

Electron-transfer oxidation of 2,6-di-tert-butyl-4-methylphenol (ArOH, 1) by matrix (RHal) radical cations (RHal=Freon-113, Bu(5)Cl and Bu(i)Cl) results in the formation of the radical cation ArOH.+ (2) as a primary intermediate directly observed during EPR and W-VIS optical absorption measurements at 77 K. In the glassy matrix of Bu(5)Cl the radical cation ArOH.+ exhibits a broad absorption band with lambda(max) = 450 nm (epsilon/dm(3) mol(-1) cm(-1) 2.1 x 10(3)). The EPR spectrum of ArOH.+ at 77 K is characterised by isotropic splitting from the freely rotating CH3 group and anisotropic splitting from the hydrogen atom in the OH group. Upon warming in the temperature range 77-103 K, deprotonation of ArOH.+ and dedeuteriation of its deuterium-substituted analog ArOD.+ resulting in the formation of the 2,6-di-tert-butyl-4-methylphenoxyl radical ArO. (4), was directly observed by EPR and optical absorption measurements in all matrices studied.