Esr Studies of Some Crowded Free Radicals Derived from Oxalate Esters
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Abstract The temperature independent esr spectrum of di-i-Propyl-t-butylmethyl radical, derived from photolysis of oxalate ester, indicates a frozen “cogwhell” conformation for this specie. The neo-pentyl substituted oxalate esters are suggested to qive β-hydrogen abstraction on presence of di-t-butylperoxide on photolysis.Keywords:
Hydrogen atom abstraction
Ultraviolet
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Hydrogen atom abstraction
Hydrogen atom
Abstraction
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Silylene
Flash photolysis
Ultraviolet
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Abstract The kinetics and mechanism of the photochemical reactions of the peroxide radicals have been investigated in polytetrafluorethylene by electron paramagnetic resonance. Under irradiation by UV light, with λ < 300 nm, the peroxide radicals ˜CF 2 CF(O 2 )CF 2 ∼ and ∼CF 2 CF 2 O 2 are dissociated and the end fluoralkyl radicals ∼CF 2 CF 2 are produced. The activation effective energy of the photodissociation of the peroxide radicals is equal to approximately 1‐2 kcal/mole. Quantum yield of the dissociation of peroxide radicals is equal to about 1. In the presence of oxygen the photorecombination of the peroxide radicals takes place. The photorecombination of the peroxide radicals bring about a reversal of the reactions of the dissociation of the end peroxide radicals and the addition of oxygen to the end fluoralkyl radical. Due to a dependence upon the initial concentration of peroxide radicals, the quantity of molecules of CF 2 O produced varies from 25 to 45 per one vanished radical. The rate of the photorecombination of the peroxide radical is in linear dependence on light intensity and in the interval 150‐500 torr does not depend upon oxygen pressure.
Peroxide
Organic peroxide
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Photodegradation
Hydroxyl radical
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Chromophore
Degradation
Bond cleavage
Visible spectrum
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This chapter contains sections titled: Introduction Formation of Phenoxyl Radicals Oxidation of Phenols by Metal Ions Oxidation of Phenols by Free Radicals Oxidation of Phenols by Radical Cations Reaction of Phenols with Hydroxyl Radicals. The Addition/Elimination Mechanism Formation of Phenoxyl Radicals by Oxidative Replacement of Substituents Formation of Phenoxyl Radicals by Intramolecular Electron Transfer Formation of Phenoxyl Radicals from Phenols and Hydroxyphenols by Reaction with O2 and/or O2·− (Autoxidation) Properties of Phenoxyl Radicals Electron Spin Resonance Spectra of Phenoxyl Radicals Phenoxyl and Monosubstituted Phenoxyl Radicals Phenoxyl Radicals with Extended π-systems Kinetic ESR Measurements Comparison with Isoelectronic Radicals Optical Spectra of Phenoxyl Radicals Acid–Base Equilibria of Phenoxyl Radicals Reactions of Phenoxyl Radicals Reduction Potentials of Phenoxyl Radicals References
Autoxidation
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Free radicals formed during the photolysis of solutions containing di-t-butyl peroxide and fluoro-acetals such as 1,1-diethoxy-2-fluoroethane and substituted 1,3-dioxolanes, have been studied by e.s.r. Spectroscopy. Only the radicals formed initially by hydrogen abstraction were detected, although product analysis by g.c.–m.s. Indicated that certain of the cyclic radicals rearranged to acyclic species. The e.s.r. Parameters are discussed in relation to the preferred conformations of the radicals.
Hydrogen atom abstraction
Peroxide
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