Oxidation of Hindered Phenols. VII. Solvent Effects on the Disproportionation of Certain Phenoxy Radicals

1959 ◽  
Vol 81 (5) ◽  
pp. 1176-1180 ◽  
Author(s):  
Clinton D. Cook ◽  
Bruce E. Norcross
Keyword(s):  
Solvent Effects ◽  
Hindered Phenols ◽  
Phenoxy Radicals

Notes: Oxidation of Hindered Phenols. IX. Equilibria Between Phenoxy Radicals

1959 ◽  
Vol 24 (9) ◽  
pp. 1356-1358 ◽  
Author(s):  
Clinton Cook ◽  
Corrine Depatie ◽  
Edwin English
Keyword(s):  
Hindered Phenols ◽  
Phenoxy Radicals

Solvent effects on the infra-red spectra of hindered phenols

1960 ◽  
Vol 254 (1276) ◽  
pp. 119-128 ◽  
Keyword(s):  
Solvent Effects ◽  
Steric Hindrance ◽  
Dynamic Equilibrium ◽  
Solvent Molecule ◽  
Thermal Agitation ◽  
Oh Groups ◽  
Infra Red ◽  
Hindered Phenols ◽  
Hindered Phenol ◽  
In Transit

The effects of variation in the shapes of the solvent and solute molecules have been studied in the hindered phenol series. When a solvent/solute complex is broken by thermal agitation it seems that reassociation of the phenolic OH with another solvent molecule occurs very rapidly. However, the introduction of bulky substituents in the immediate neighbourhood of the OH group lengthens the time between collisions suitably oriented for association. It then becomes possible to detect free OH absorptions corresponding to solute molecules in transit from one molecular association to another. These occur even in such strongly bonding solvents as ethers, and the proportions increase with the complexity of the hindering groups. Similar effects are found when a hindered phenol is examined in a series of solvents of increasing complexity, confirming that there is a dynamic equilibrium between free and associated OH groups. The OH group in the hindered phenols is largely coplanar and only in the 2,6-di- tert. -butyl derivative is there any direct steric hindrance to the approach of the solvent molecule.

Oxidation of Hindered Phenols. IV. Stable Phenoxy Radicals

1956 ◽  
Vol 78 (9) ◽  
pp. 2002-2005 ◽  
Author(s):  
Clinton D. Cook ◽  
David A. Kuhn ◽  
Peter Fianu
Keyword(s):  
Hindered Phenols ◽  
Phenoxy Radicals

Reactivity of Peroxy Radicals Coordinated to Vitamin B12 Studied by Electron Spin Resonance Spectroscopy

2004 ◽  
Vol 69 (11) ◽  
pp. 2091-2097 ◽  
Author(s):  
Alexander Tkáč ◽  
Eva Hanušovská
Keyword(s):  
Peroxy Radical ◽  
Resonance Spectroscopy ◽  
Vitamin B ◽  
Sterically Hindered Phenols ◽  
Peroxy Radicals ◽  
Oh Groups ◽  
Biological Targets ◽  
Hindered Phenols ◽  
Phenoxy Radicals ◽  
Radical Attack

One-electron transfer from chelated Co(II)(3d7) of vitamin B12 (cyanocobalamine) to tert-butylhydroperoxide forms at ambient temperature in non-polar solvents peroxy radicals stabilized by π-coordination to Co(III)(3d6) of the oxidized vitamin. In the absence of oxygen, the peroxy radicals manifest themselves as singlet ESR lines at g = 2.0174. After addition of sterically hindered phenols, apart from the decreased original singlet line, a new signal of stable phenoxy radicals, formed by H-abstraction from the phenols, is observed. Phenoxy radicals generated from unhindered phenols remain stabilized by σ-coordination to the cobalt(III) centre, giving rise to an ESR signal split into eight lines due to interaction of the unpaired electron with the magnetic moment of the 59Co nucleus (I = 7/2) of vitamin B12. Large molecules with unhindered OH groups, such as testosterone or cholesterol cannot be coordinated after the primary radical attack and the generated radicals disappear by recombination. By this technique, the sensitivity of biological targets to primary peroxy radical attack as well as the efficiency of different antioxidants (vitamin E, Stobadine) can be tested.

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