Free radicals . See

Aldehydes are important because they are temporary reservoirs of free radicals (see eqs. 11 and 12). HCHO is a known carcinogen. Nitric acid is formed by OH attack on NO2 and by a dark-phase series of reactions initiated by O3 + NO2. Nitric acid is important because it is the second most abundant acid in precipitation. In addition, in southern California it is the major cause of acid fog. 

For reviews of the use of ESR spectra to determine structures, see Walton, J.C. Rev. Chem. Intermed., 1984, 5, 249 Kochi, J.K. Adv. Free-Radical Chem., 1975, 5, 189. For ESR spectra of a large number of free radicals, see Bielski, B.H.J. Gebicki, J.M. Atlas of Electron Spin Resonance Spectra Academic Press NY, 1967. 

A photolytic cleavage can break the molecule into two smaller molecules or into two free radicals (see p. 318). Cleavage into two ions, though known, is much rarer. Once free radicals are produced by a photolysis, they behave like free radicals produced in any other way (Chapter 5) except that they may be in excited states, and this can cause differences in behavior. 

There is much evidence" for this mechanism, including side products (RH, alkenes) characteristic of free-radical intermediates and the fact that electrolysis of acetate ion in the presence of styrene caused some of the styrene to polymerize to polystyrene (such polymerizations can be initiated by free radicals, see p. 978). Other side products (ROH, RCOOR) are sometimes found these stem from further oxidation of the radical R to the carbocation... 

Thermal insertion occurs at room temperature when R is XCH2CHAr-, at 40° C when R is benzyl, allyl, or crotyl (in this case two isomeric peroxides are formed), but not even at 80° C when R is a simple primary alkyl group. The insertion of O2 clearly involves prior dissociation of the Co—C bond to give more reactive species. The a-arylethyl complexes are known to decompose spontaneously into CoH and styrene derivatives (see Section B,l,f). Oxygen will presumably react with the hydride or Co(I) to give the hydroperoxide complex, which then adds to the styrene. The benzyl and allyl complexes appear to undergo homolytic fission to give Co(II) and free radicals (see Section B,l,a) in this case O2 would react first with the radicals. 

Aromatic rings are moderately reactive toward addition of free radicals (see Part A, Section 12.2) and certain synthetically useful substitution reactions involve free radical substitution. One example is the synthesis of biaryls.175... 

Salts and complexes of transition metals accelerate hydrocarbon oxidation due to the catalytic decomposition of hydroperoxides to free radicals (see Chapter 10). 

Deactivation of the Mediator Deactivation of the mediator is a commonly encountered event in the practice of homogeneous catalysis. Among the various ways of deactivating the mediator, the version sketched in Scheme 2.10 is particularly important in view of its application to the determination of the redox characteristics of transient free radicals (see Section 2.7.2).14 The current-potential responses are governed by three dimensionless parameters, 2ei = /F)(ke Cjl/v), which measures the effect of the rate-determining... 

Some of these factors contain metal ions as redox-active components. In these cases, it is usually single electrons that are transferred, with the metal ion changing its valency. Unpaired electrons often occur in this process, but these are located in d orbitals (see p.2) and are therefore less dangerous than single electrons in non-metal atoms ( free radicals see below). 

Reaction of atoms and free radicals (see references cited in Jonah et al. [9]). 

For a discussion of the general properties and reactivity of free radicals see F. A. Carey and R. J. Sundberg, Advanced Organic Chemistry, Part A Structure and Mechanisms, 3rd ed., Plenum, New York, 1990, Chapter 12, pp. 651-708. 

Direct substitution reactions of other diamonoid hydrocarbons have not been studied extensively. Triamantane, for example, remains relatively unavailable at this time. Moreover, the low symmetry of this molecule discourages attempts to prepare triamantane derivatives by direct substitution. The highly selective ionic reactions would most certainly not give all possible isomers. Less selective substitutions (e.g. free radical, see below), on the other hand, might enable the preparation of most isomers but separation of the product mixtures would undoubtedly be extremely tedious. 

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