Aliphatic free radicals

Although the work of Gomberg and those who followed provided good evidence for the existence of arylmethyl radicals, there was still skepticism regarding simple aliphatic radicals such as methyl and ethyl. As noted above, the modern history of these species began with the suggestions of Crum Brown (equation 2).  

This technique was quickly adopted by others and it was soon found by F.O. Rice and co-workers that the pyrolysis of many organic compounds at 800 to 1000°C removed metallic mirrors, implicating the formation of free radicals. The cleavage of larger free radicals into smaller radicals and olefins under these conditions, was also proposed (equation 22), as well as chain reactions in which radicals abstract hydrogen from alkanes. Reactions of alkyl halides with metal atoms in the gas phase were also found by M. Polanyi and co-workers to yield alkyl radicals (equation 23). 

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Ruchardt, C. et al. Structure Reactivity-Relationships in the Chemistry of Aliphatic Free Radicals. XXIII. Intemat. Congr. Pure and Appl. Chemistry, Vol. 4, p. 223. Special Lectures, London Butterworths 1971... 

Rice, F. O., Rice, K. K., The Aliphatic Free Radicals, Johns Hopkins, Baltimore,... 

Freiberg M, Meyerstein D (1980) Reactions of aliphatic free radicals with copper cations in aqueous solution, part 2. Reactions with cupric ions a pulse radiolysis study. J Chem Soc Faraday Trans 176 1825-1837... 

Rice and Rice, The Aliphatic Free Radicals, The Johns Hopkins Press, Baltimore (1935). 

Free radical chain reactions 12 Aliphatic free radicals 12... 

For a resum6 of this early work, see F. O. Rice and K. K. Rice, The Aliphatic Free Radicals, The Williams Wilkins Company, Baltimore, 1935. A more general treatise on free radicals will be found in E. W. R. Steacie, Atomic and Free Radical Reactions, A.C.S. Monograph No. 125, 2d ed., Reinhold Publishing Corporation, New York, 1954. 

Kolbe Reaction Anodic Oxidation of Carboxylates Coupling of Aliphatic Free Radicals... 

In reactions of divalent transition metal ions with aliphatic free radicals, metal-carbon a-bond formation is formally accompanied by oxidation of the MC ... 

W.A. Mulac and D. Meyerstein, Reactions of B,2r with Aliphatic Free Radicals A Pulse Radiolysis Study, J. Am. Chem. Soc., 104 (1982) 4124. 

Pulsed amperometric detection is used for the direct detection of a variety of polar aliphatic compounds, many of which, like carbohydrates, peptides and sulfur-containing compounds are of biological interest [171,197-200]. Most aliphatic compounds are not amenable to constant potential amperometric detection. Free-radical products from the oxidation of aromatic molecules can be stabilized by it-resonance hence the activation barrier for reaction is decreased. This mechanism is unavailable for stabilizing aliphatic free radicals. The activation barrier for oxidation of aliphatic compounds can be decreased at noble-metal electrodes with partially unsaturated d-orbitals (e.g. gold, platinum) that can adsorb and thereby stabilize free radical oxidation products and intermediates. Carbon electrodes are not electrocatalytic and are unsuitable for pulsed amperometric detection. 

Table II lists representative yield data for H2S- and 02-scavenged CH3CHF2. Within the limiting statistical accuracy, at fixed (P/Z) most of the yields are the same with either scavenger. Aliphatic free radicals react rapidly with both O2 and H2S. Therefore, observations of yield insensitivity to the presence of these scavengers preclude the mechanistic involvement of labeled alkyl radicals.

Rice, F.O. and K.K. Rice, 1935, The aliphatic free radicals (John Hopkins Press, Baltimore) p. 58. 

Carbon-Cobalt(iii) Bonds.—These bonds are readily formed in reactions of aliphatic free radicals with Co complexes. Reaction of CHgOH, MeCHOH, HOCHCH2OH, or CHaCHO with the macrocyclic complex [Co K2)J produces the unstable intermediate [Co (2)—RH] containing a cr-carbon-cobalt bond ... 

The reaction between oiganochromium macrocycle complexes of the type [CrR(OH2)(L ] and I2 gives [CrR(OH2)L] aiul F. The kinetic data are consistent with a chain mechanism iititiated by election transfer. The aliphatic free radical CHMeCH(OH)Me reacts with Cr (aq) to form a... 

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