- Electron Paramagnetic Resonance Spectra of Aliphatic Ketyl Radical Anions in Fluid Solution
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Improved methods have been developed for generating aliphatic ketyl radical anions in solution for study by EPR spectroscopy.These methods involve either photolysis of a solution of potassium in the corresponding alcohol (which probably proceeds by initia
- Davies, Alwyn G.,Neville, Anthony G.
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- Quantitative rate constants for radical reactions in the nanopores of cotton
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The understanding of radical reactions in nanostructured materials is important for developing new synthetic procedures and controlling degradation reactions. To develop this area, an easy method for measuring quantitative rate constants of some radical r
- Hunt, Paula,Worrall, David R.,Wilkinson, Frank,Batchelor, Stephen N.
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- The thermal charge-transfer reduction of uranyl UO22+(VI) to UO2+(V) by various functionalized organic compounds, and evidence for possible spin-spin interactions between UO2+(V) and hydroxymethyl ([rad]CH2OH) radical and between UO2+(V) and diphenyl sulfide radical cation (Ph2S[rad]+)
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The linear uranyl UO22+(VI) cation (D∞h symmetry) exhibited strong and broad absorptions at 350–400 nm in anhydrous methanol and methanol-water mixtures in the UV-Vis spectra. The intensity of the absorptions (represented by absorbance at 375 nm) is directly proportional to molar concentrations of methanol and UO22+(VI), respectively. The linear relationships indicate formation of an electron-donor-acceptor (EDA) complex [UO22+, CH3OH]. The absorptions at 350–400 nm originate from the charge-transfer (single-electron transfer) from CH3OH (electron donor) to UO22+ (electron acceptor) within the [UO22+, CH3OH] complex. Electron paramagnetic resonance (EPR) studies of various mixtures of UO22+-CH3OH and UO22+-CH3OH-H2O have shown that the charge-transfer also took place slowly in the dark, resulting in thermal reduction of UO22+(VI) to UO2+(V) (singlet, g = 2.08) by CH3OH, and CH3OH was oxidized to the hydroxymethyl [rad]CH2OH radical (generating an axial signal). The charge-transfer oxidation-reduction reaction is believed to take place via the EDA [UO22+, CH3OH] complex. EPR studies suggested spin-spin coupling between UO2+(V) and [rad]CH2OH in anhydrous methanol, supporting the formation of a [UO2+, [rad]CH2OH] ion-radical pair. The EPR studies have also shown that UO22+(VI) was reduced to UO2+(V) thermally by other alcohols (ethanol, 2-propanol, and cyclohexanol), and by diphenyl sulfide (Ph2S), L-ascorbic acid (AA), and 2-methyl-5-(propan-2-yl)phenol (carvacrol, ArOH), respectively. Ph2S, AA, and ArOH were oxidized to the diphenyl sulfide Ph2S+[rad] radical cation (singlet, g = 2.00), ascorbic acid AA[rad] radical (singlet, g = 2.00), and carvacrol ArO[rad] radical (singlet, g = 1.98), respectively. Both EPR and UV-Vis studies indicate that the reactions followed the ground-state charge-transfer mechanisms similar to that of the UO22+/methanol reaction. EPR evidence supported formation of the [UO2+, Ph2S+[rad]] ion-radical pair in the charge-transfer reaction of UO22+ and Ph2S and spin-spin interactions within the ion-radical pair. The sulfuric-acid-catalyzed isomerization of [rad]CH2OH to CH3O[rad] was found by EPR studies.
- Sun, Xiaoping,Kolling, Derrick R.J.,Deskins, Seth,Adkins, Ethan
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- Probing the reactivity of photoinitiators for free radical polymerization: Time-resolved infrared spectroscopic study of benzoyl radicals
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A series of substituted benzoyl radicals has been generated by laser flash photolysis of α-hydroxy ketones, α-amino ketones, and acyl and bis(acyl)phosphine oxides, all of which are used commercially as photoinitiators in free radical polymerizations. The benzoyl radicals have been studied by fast time-resolved infrared spectroscopy. The absolute rate constants for their reaction with n-butylacrylate, thiophenol, bromotrichloromethane and oxygen were measured in acetonitrile solution. The rate constants of benzoyl radical addition to n-butylacrylate range from 1.3 x 105 to 5.5 x 105 M-1 s-1 and are about 2 orders of magnitude lower than for the n-butylacrylate addition to the counterradicals that are produced by α-cleavage of the investigated ketones. Density functional theoretical calculations have been performed in order to rationalize the observed reactivities of the initiating radicals. Calculations of the phosphorus-centered radicals generated by photolysis of an acyl and bis(acyl)phosphine oxide suggest that P atom Mulliken spin populations are an indicator of the relative reactivities of the phosphorus-centered radicals. The α-cleavage of (2,4,6-trimethylbenzoyl)phosphine oxide was studied by picosecond pump-probe and nanosecond step-scan time-resolved infrared spectroscopy. The results support a mechanism in which the α-cleavage occurs from the triplet excited state that has a lifetime less than or equal to the singlet excited state.
- Colley, Christopher S.,Grills, David C.,Besley, Nicholas A.,Jockusch, Steffen,Matousek, Pavel,Parker, Anthony W.,Towrie, Michael,Turro, Nicholas J.,Gill, Peter M. W.,George, Michael W.
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p. 14952 - 14958
(2007/10/03)
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- Electron Spin Resonance Study of Inversion and Conformations in 1-Hydroxycyclohexyl Radicals
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We have obtained the variable-temperature e.s.r. spectra of the 1-hydroxycyclohexyl, 4-methyl-1-hydroxycyclohexyl, and 4-t-butyl-1-hydroxycyclohexyl radicals by photolysis of the precursor alcohols mixed with di-t-butyl peroxide.From computer analysis of
- Lloyd, Roger V.,Causey, J. Guy
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p. 1143 - 1147
(2007/10/02)
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