Radicals inorganic

The study of surface-stabilized inorganic radicals by EPR has a long history. This partially arises from their ease of generation and their favorable stabihty on the ionic oxide surfaces. From a catalysis point of view, such radicals are fundamentally important, since they can act as intermediates or oxidants in the catalytic cycle. If isotopic substitution of the radical is facile, then a very thorough description of the electronic and geometric properties of the species can once again be obtained by analysis of the powder EPR pattern. 

Simulation of the spectrum, revealed that at least two different C02 radicals are present (i.e. with two different sets of g and A tensors), suggesting that two different surface sites must be available for stabilizing the species. For convenience, only the spectroscopic properties of the most dominant species will be presented here. The experimental g and A tensors were found to be = 2.0026, g = 1.9965, g, = 2.0009, = 507.5, Aj,, = 495.2 and A = 629.3 MHz. The 

The large isotropic component is due to the unpaired electron spin density in the carbon 2s orbital, and this value (544MHz) can be used to derive an estimate of the carbon 2 s orbital contribution to the molecular orbital. Since the theoretical isotropic coupling constant for is 3777MHz, then C2s = 544/3777 = 0.144. The anisotropic dipolar part of the hyperfine arises from unpaired spin density in the 2p orbital. However because the dipolar contribution in Equation 1.52 cannot be reduced to zero, this implies that a fraction of the spin density is allocated to the 2p orbital perpendicular to the molecular plane. Therefore, the dipolar component of Equation 1.52 must be further decomposed into two symmetrical tensors oriented along the z and x axes  

This information may be interpreted in terms of the unpaired electron being confined to a carbon sp hybrid orbital (4ai) built up by carbon 2s and 2p and oxygen 2p atomic orbitals. The 2pj character of the 4ai molecular orbital can be estimated by comparison with the integral  

In addition to the study of the (H )(e )/N2 system, a detailed analysis of the analogous (H )(e )/02 complex was also reported, with particular emphasis on the hyperfine structure of adsorbed O) [44, 45]. The Fermi contact term was evaluated as ajs = -20.3 G and the resulting dipolar tensor was found to be Bxx = -56 G, Byy = 4-27.5 G, B z = -I-28.6G. These values were later confirmed by 

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In addition to inorganic radicals, which profoundly modify the properties of a paraflSn hydrocarbon residue, there is a whole series of organic groupings which are distinguished by exceptional reactivity, for example, the ethylene and acetylene groupings, and the phenyl and naphthyl radicals. Thus the characterisation of unsaturated hydrocarbons and their derivatives, e.g., the aromatic compounds, becomes possible. 

P. B. Ayscough, Electron Spin Resonance in Chemistry, pp. 300-1, Methuen, London, 1967. P. W. Atkins and M. C. R. Symons, The Structure of Inorganic Radicals, pp. 51-73, Elsevier, Amsterdam, 1967. 

Ross, A. B. and Neta, P. "Rate Constants for Reactions of Inorganic Radicals in Aqueous Solutions", NSRDS-NBS65, U. S. Government Printing Office, Washington, D.C., 1979. 

P.W. Atkins and M.C.R. Symons, The Structure of Inorganic Radicals, Elsevier, Amsterdam, 1967. 

In their 1967 book, Atkins and Symons6a summarized much of the early ESR work on small inorganic radicals, many of which were produced by photolysis or radiolysis of single crystals of the precursor molecules. A good example of the application of the information that can be obtained from such single-crystal studies is the analysis of the spectrum of N03, produced by y-irradiation of KN03 crystals by Livingston and Zeldes.6b Table 4.1 summarizes the results. 

In aqueous solution the electron transfer between (reducing) carbon-centered radicals or (oxidizing) hetero-atom-centered inorganic radicals and organic molecules often proceeds by covalent bond... 

To this solution is added 90 g. (0.33 mole) of potassium nitroso-disulfonate (Fremy s salt) (Note 2). The mixture is shaken to dissolve the inorganic radical. A solution of 16 g. (0.131 mole) of 3,4-dimethylphenol (Note 3) in 350 ml. of ether is added quickly to the purple solution. The mixture is shaken vigorously for 20 minutes (Note 4). The color of the solution changes to red-brown. The o-quinone thus formed is subsequently extracted in three portions with a total of 1.2 1. of chloroform. The combined organic layers are dried over anhydrous sodium sulfate (Note 5), filtered, and evaporated under reduced pressure at 20-23° (Note 6). The residual, somewhat oily red-brown crystals are slurried twice with 15 ml.-portions of ice-cold ether and collected on a filter. The remaining dark red crystals, after air drying, weigh 8.7-8.9 g. (49-50%), m.p. 105-107° (Note 7). 

CgQ is a radical sponge (Scheme 14.4) and readily adds organic as well as inorganic radicals (see Chapter 6). As with nucleophilic additions, multiple additions take place if an access of radicals is allowed to react with the fullerene. 

More selective oxidizing conditions can be achieved by converting OH into another inorganic radical (e.g., Br, Ij, (SCN), CO, Nj, etc.), thereby tuning the reduction potential (see Table 6). One of the most powerful oxidizing radicals is 804 , which is produced in reaction (69) ... 

Secondary inorganic radicals are particularly useful for studying redox changes in metalloproteins and organometallic complexes because these radicals are more likely to react at the metal center by electron transfer, whereas OH will also attack the organic moiety and, by abstracting H, create a reducing radical there. 

Tabie 6 Reduction Potentials of Some Inorganic Radicals... 

Neta, P., R. E. Huie, and A. B. Ross, Rate Constants for Reactions of Inorganic Radicals in Aqueous Solution, . /. Phys. Chem. Ref. Data, 17, 1027-1228 (1988). 

Nitrogen monoxide has held the attention of scientific community from the time this small inorganic radical was discovered to play a... 

Pseudohalogens There arc certain inorganic radicals which have the properties of existing either as... 

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