Activation parameters for the restricted rotation of the hydroxyl group in the duroquinol cation radical as determined from the electron spin resonance spectra

1974 ◽  
Vol 78 (2) ◽  
pp. 130-134 ◽  
Author(s):  
Daniel G. Ondercin ◽  
Paul D. Sullivan
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Cation Radical ◽  
Activation Parameters ◽  
Hydroxyl Group ◽  
Restricted Rotation ◽  
Spin Resonance

Determination of the Rates of Ring-Closure of Oxygen-Containing Analogs of Hex-5-Enyl Radical by Kinetic Electron Spin Resonance Spectroscopy

1987 ◽  
Vol 40 (1) ◽  
pp. 157 ◽  
Author(s):  
ALJ Beckwith ◽  
SA Glover
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Activation Parameters ◽  
Ring Closure ◽  
Electron Spin Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Restricted Rotation ◽  
Conformational Effects ◽  
Spin Resonance

The hex-5-enyl (1), 3-oxahex-5-enyl (6), 2-oxahex-5-enyl (9) and 2,2-dimethylbut-3- enoyloxymethyl (13) radicals have been generated by interaction of the corresponding bromides with trialkyltin or trialkylgermanium radicals, and their rate constants and activation parameters for cyclization have been determined by kinetic e.s.r . spectroscopy. The 3-oxa species (6) undergo 1,5-ring closure more rapidly than does hex-5-enyl radical (1) because of favourable stereoelectronic factors. Spectral evidence has been obtained for restricted rotation about the O-CH2* bond in the 2-oxa radical (9) as a consequence of which its ring closure is relatively slow. Similarly, 1,5-ring closure of the ester derived radical (13) is slow because of unfavourable conformational effects arising from restricted rotation about the CO-O bond. The radical (22) formed from allyl bromoacetate does not undergo ring closure. Spectral data have been obtained for various radicals (16), (19), (23), (24) formed by intermolecular addition.

Analysis of line-width effects in the electron spin resonance spectra of monoprotonated semiquinones

1969 ◽  
Vol 47 (2) ◽  
pp. 331-337 ◽  
Author(s):  
T. E. Gough
Keyword(s):  
Electron Spin Resonance ◽  
Line Width ◽  
Electron Spin ◽  
Energy Of Activation ◽  
Hydroxyl Group ◽  
Restricted Rotation ◽  
Spin Resonance

Electron spin resonance spectra of monoprotonated p-benzosemiquinone, 2:6-dimethyl-p-benzosemiquinone, and durosemiquinone dissolved in tetrahydrofuran at −70 °C are reported. Under such conditions restricted rotation of the hydroxyl group causes the ring positions meta to the site of protonation to appear as non-equivalent, though this effect is not observed for monoprotonated durosemiquinone. The spectra of monoprotonated p-benzosemiquinone in tetrahydrofuran exhibit both anisotropic and alternating line-width trends; equations are presented which allow the separation of these two effects and the determination of the energy of activation for the rotation of the hydroxyl group as between 31 and 40 kJ/mole. Spectra of monoprotonated 2:3- and 2:5-dimethyl-p-benzosemiquinones in 1:2 dimethoxyethane at 20 °C are also reported.

ORGANIC AND BIOLOGICAL SPECTROCHEMICAL STUDIES: XXIII. CONFORMATION OF THE p-DIMETHOXYBENZENE CATION RADICAL IN CONCENTRATED SULFURIC ACID

1966 ◽  
Vol 44 (13) ◽  
pp. 1501-1512 ◽  
Author(s):  
W. F. Forbes ◽  
P. D. Sullivan
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Electron Spin Resonance ◽  
Sulfuric Acid ◽  
Magnetic Resonance ◽  
Electron Spin ◽  
Cation Radical ◽  
Molecular Orbital Calculations ◽  
Spin Resonance ◽  
Concentrated Sulfuric Acid ◽  
Nuclear Magnetic

The electron spin resonance spectrum of the p-dimethoxybenzene cation radical in concentrated sulfuric acid is interpreted in terms of cis–trans isomerism. Empirical molecular orbital calculations support these assignments. The two isomers are found to possess slightly different "g" values, Δg (cis – trans) being ca. 1.8 × 10−5.Nuclear magnetic resonance and ultraviolet data show that the radical exists in equilibrium with the neutral non-radical species at room temperature, but that sulfonation occurs at higher temperatures. Nuclear magnetic resonance and electron spin resonance data of solutions of p-dimethoxybenzene in D2SO4 show that rapid exchange of the ring protons occurs.

FREE RADICALS OF BIOLOGICAL INTEREST: I. ELECTRON SPIN RESONANCE SPECTRA OF TOBACCO SMOKE CONDENSATES

1967 ◽  
Vol 45 (7) ◽  
pp. 1087-1098 ◽  
Author(s):  
W. F. Forbes ◽  
J. C. Robinson ◽  
G. F. Wright
Keyword(s):  
Free Radicals ◽  
Electron Spin Resonance ◽  
Sulfuric Acid ◽  
Electron Spin ◽  
Tobacco Smoke ◽  
Cation Radical ◽  
Fold Increase ◽  
Active Centers ◽  
Radical Species ◽  
Spin Resonance

Smoke condensates, prepared from tobacco smoke, are shown to contain a variety of paramagnetically active centers. Some of these have lifetimes of a few seconds. Smoke condensates, when dissolved in sulfuric acid, give rise to at least two cation radical species. The more short-lived species may be the anthracene or an anthracene-type cation radical species and the more long-lived one may be a cation radical related to, but not identical with, the 3,4-benzpyrene cation radical.When 3,4-benzpyrene is heated to near its melting point, considerably more intense electron spin resonance (e.s.r.) spectra are obtained. The heated benzpyrene sample, when dissolved in sulfuric acid, also gives a more intense, but otherwise similar, spectrum than an unheated sample. These observations indicate that, on heating benzpyrene, additional free radicals are formed, and this may account for the relatively high carcinogenicity of tobacco smoke condensates.The e.s.r. spectrum of 3,4-benzpyrene in sulfuric acid undergoes an approximately 10-fold increase in signal intensity when similar amounts of 3,4-benzpyrene-6,7-quinone are added to the mixture. The latter compound on its own does not afford a detectable signal under these conditions. This indicates that the ability of known carcinogenic substances, such as 3,4-benzpyrene, to give rise to free-radical species can be appreciably affected by the molecular environment.

Electron Spin Resonance Study of Surface Defects of Silica Gel Formed by Gas Discharges

1971 ◽  
Vol 49 (3) ◽  
pp. 352-356 ◽  
Author(s):  
K. Hukuda ◽  
Y. Amenomiya
Keyword(s):  
Electron Spin Resonance ◽  
Silica Gel ◽  
Electron Spin ◽  
Surface Defects ◽  
Hydroxyl Group ◽  
Electron Spin Resonance Study ◽  
Gas Discharges ◽  
Spin Resonance ◽  
Magnetic Center ◽  
Spin Resonance Study

Surface defects of silica gel formed by a microwave electric discharge in a stream of oxygen and of nitrogen have been studied by means of electron spin resonance (e.s.r.) spectroscopy. The magnetic center is identified as a hole trapped by a surface oxygen atom which is formed by the removal of a hydrogen atom from a hydroxyl group. The principal values of the g-tensor were found to be gxx = 2.037, gyy = 2.008, and gzz = 2.002, respectively, where the direction of x-axis was taken along the O—Si bond. The center has a weak hyperfine interaction with a hydrogen nucleus of an adjacent hydroxyl group. The hyperfine splitting is 15 Oe.

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