Free electron transfer from several phenols to radical cations of non-polar solvents

Abstract

Electron-transfer reactions from phenols to parent radical cations of solvents were studied using pulse radiolysis. Phenols bearing electron-withdrawing, electron-donating and bulky substituents were investigated in non-polar solvents such as cyclohexane, n-dodecane, n-butyl chloride and 1,2-dichloroethane. The experiments revealed the direct, synchronous formation of phenoxyl radicals and phenol radical cations in all cases and in nearly the same relative amounts. This was explained by two competing electron-transfer channels which depend on the geometry of encounter between the parent solvent radical cations and the solute phenol molecules. The mechanism is analysed at a microscopic level, treating di †usion as a slow process and the local electron transfer as an extremely rapid event. Furthermore, the e †ect of various phenol substituents and solvent types on the electron-transfer mechanism and on the decay kinetics of the solute phenol radical cations was analysed. The results were further substantiated using a quantum chemical approach.

Radiation Chemistry in Chemically Amplified Resists

“…155) For p-cresol, the absorption coefficients of the phenoxy radical and radical cation are 2:30 Â 10 3 and 2:88 Â 10 4 M cm À1 at each peak wavelength, respectively. 169) For the other phenol derivatives, the absorption coefficients of radical cations observed at 400 -600 nm are generally larger than those of phenoxy radicals observed at 400 -500 nm. Therefore, the radical cation of PHS is considered to be mostly deprotonated 200 ns after the pulse.…”

“…158,[161][162][163][164][165][166][167][168] The absorption maxima of radical cations of phenol and p-cresol are at 440 and 430 nm, respectively. 169) The radiation chemistry of the model compounds for protected PHS such as methoxybenzene (anisole), methoxytoluene, and dimethoxybenzene has also been intensively investigated using pulse radiolysis, [170][171][172][173] photolysis, 174,175) chemical oxidation, [176][177][178] and electrochemical methods. 179,180) Radical cations of p-methoxytoluene are observed at 440 175) and 450 nm 174) in acetonitrile and at 460 nm in 1,2-dichloroethane.…”

Exploring Autoionization and Photoinduced Proton-Coupled Electron Transfer Pathways of Phenol in Aqueous Solution

“…1(b). These data reveal an additional feature centered at 425 nm (indicated by the arrow), which we assign based on prior literature, 21,[27][28][29] to the ground state phenol radical cation (PhOH •+ ), and which disappears on a sub-picosecond timescale. To the best of our knowledge, this represents the first observation of the PhOH •+ species in aqueous solution near neutral pH.…”

Reprint of “Hurdles and pitfalls in measuring antioxidant efficacy: A critical evaluation of ABTS, DPPH, and ORAC assays”

“…While the end result of the two mechanisms may be the same, kinetics and dependence on system conditions, especially solvent and pH, vary tremendously. Electron transfer is very fast (femtoseconds) (Ganapathi, Hermann, Naumov, & Brede, 2000), it is not diffusion-controlled, and it increases with pH as ionization increases availability of electrons. Hydrogen atom transfer, in contrast, is considerably slowed by diffusion; it is independent of pH but strongly enhanced by water and inhibited by hydrogen bonding solvents such as alcohols.…”