THE ELECTRON-SPIN RESONANCE SPECTRA OF SOME METHYLATED ANTHRASEMIQUINONES: EVIDENCE FOR RESTRICTED ROTATION

1965 ◽  
Vol 43 (5) ◽  
pp. 1553-1559 ◽  
Author(s):  
R. M. Elofson ◽  
K. F. Schulz ◽  
B. E. Galbraith ◽  
R. Newton
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Steric Hindrance ◽  
Methyl Groups ◽  
Redox Potentials ◽  
Restricted Rotation ◽  
Spin Resonance

The hyperfine electron-spin resonance spectra of a number of methyl-substituted 9,10-anthrasemiquinones have been determined. The spectra have been analyzed by computer techniques, and splitting constants have been assigned for all protons. The results indicate that, while the parent quinones are essentially free of steric hindrance, the methyl groups in the α position of the reduced quinones are not free to rotate. The methyl groups in the β position of the semiquinones show normal hyperconjugative behavior. These results are consistent with the different redox potentials of these compounds revealed in a previous study.

Electron spin resonance studies of radiation damage. Part I. An alternating linewidth effect for the (CH3)2ĊOH radical in gamma-irradiated acetone at low temperatures

1968 ◽  
Vol 46 (6) ◽  
pp. 1029-1031 ◽  
Author(s):  
F. P. Sargent
Keyword(s):  
Electron Spin Resonance ◽  
Temperature Dependence ◽  
Radiation Damage ◽  
Electron Spin ◽  
Low Temperatures ◽  
Methyl Groups ◽  
Oh Groups ◽  
Restricted Rotation ◽  
Spin Resonance ◽  
Gamma Irradiated

The e.s.r. spectrum of the (CH3)2ĊOH radical showed a drastic temperature dependence of linewidth in the range −196 to −100 °C, this being particularly pronounced for the M1 = ±2 lines. Possible mechanisms are discussed in terms of restricted rotation of the methyl groups and of the OH groups.

A PARAMAGNETIC RESONANCE STUDY OF HINDERED DIARYLMETHYL RADICALS AND RELATED COMPOUNDS: I. ANALYSIS OF THE SPECTRA

1966 ◽  
Vol 44 (12) ◽  
pp. 1387-1395 ◽  
Author(s):  
H. R. Falle ◽  
F. C. Adam
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Ion Pair ◽  
Coupling Constants ◽  
Methyl Groups ◽  
Steric Repulsion ◽  
Paramagnetic Resonance ◽  
Spin Resonance ◽  
Phenyl Rings ◽  
Related Compounds

Several ortho-substituted radicals of the benzhydryl type and a variety of diaryl ketyls have been studied through the nuclear hyperfine structure of their electron spin resonance spectra. A strong similarity is found between the spectra of a given ketyl and its hydrocarbon analogue. This suggests that when ketones are reduced, a very tight ion pair is formed between the ketyl anion and its cation. Although the coupling constants of the protons vary with different reducing agents, larger variations are observed when bulky groups are substituted into ortho positions. These larger changes are attributed to a forced internal rotation of the phenyl rings. The distortion results from the steric repulsion between the ortho groups. The effect of 'buttressing' of ortho methyl groups is also studied. Deuterium and 13C substitutions have been effected in some of the compounds.

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.

Electron Spin Resonance Studies of the Radiolysis of Aliphatic Amines at 77 °K

1971 ◽  
Vol 49 (11) ◽  
pp. 1869-1879 ◽  
Author(s):  
P. Wardman ◽  
D. R. Smith
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Aliphatic Amines ◽  
Methyl Ethyl ◽  
Alkyl Radicals ◽  
Restricted Rotation ◽  
Parallel Component ◽  
Alkyl Groups ◽  
Spin Resonance ◽  
Butyl Amine

Several frozen aliphatic amines have been γ-irradiated at 77 °K and the electron spin resonance (e.s.r.) spectra of the trapped radicals obtained at 77 °K and on warming. Radiolysis of methyl, ethyl and isopropyl amines produces predominantly alkylamino [Formula: see text] radicals. The proton hyperfine (h.f.) couplings of [Formula: see text] radicals are 10–30% larger than those in the corresponding isoelectronic alkyl radicals and the parallel component of the 14N coupling is about 35 G. Restricted rotation of alkyl groups occurs at 77 °K in some cases. On warming from 77 °K, the [Formula: see text] radicals generally abstract from the solvent or isomerize to produce radicals of the aminoalkyl type (e.g. RĊHNH2). The alkyl proton h.f. splittings of these latter radicals are 20–40% lower than in the corresponding alkyl radicals, and the observed 14N coupling was [Formula: see text] in ĊH2NR2 and [Formula: see text] in (CH3)2ĊNH2 and CH3ĊHNH2. The amino proton couplings in the aminoalkyl radicals were not resolved. Irradiated dimethylamine produces both (CH3)2N and CH2N(CH3) radicals, but (CH3)2N disappears on warming. Only ĊH2N(CH3)2 was observed after irradiation of (CH3)3N at 77 °K. Solid methoxyamine (giving CH3ONH) and tert-butyl-amine were also studied.

An electron spin resonance study of the oxidation of benzene solutions of phenols by means of silver oxide

1968 ◽  
Vol 302 (1470) ◽  
pp. 329-330
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Silver Oxide ◽  
Electron Spin Resonance Study ◽  
Methyl Groups ◽  
Substituted Phenols ◽  
Heterogeneous Oxidation ◽  
Spin Resonance ◽  
Oxidation Of Benzene ◽  
Spin Resonance Study

The heterogeneous oxidation of some substituted phenols has been studied by means of electron spin resonance. Strong signals, observed during the oxidation of the phenols with a free para -position, are due to secondary radicals derived from C 4 —O linked dimeric and polymeric phenols ( A ) are not to substituted 4, 4'-di-pheno-semiquinones ( B ). Special attention has been given to the oxidation of 2, 6-dimethylphenol which yields a radical with non-equivalent methyl groups. The e. s. r. spectra of the secondary radicals from some 4-substituted 2, 6-dimethylphenol are identical to each other and to that from 2, 6-dimethylphenol itself. This indicates that in these radicals the para -substituent had been displaced by an aryloxy group. The ease of this displacement can be determined by use of the flow technique.

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