Radicals and their reactions

Most of the reactions that have been considered to-date have involved the participation of polar reactants and intermediates, i.e. carboca-tions and carbanions, or related highly polarised species, involving the heterolytic fission, and formation, of covalent bonds  

But homolytic fission can also take place, thus generating species possessing an unpaired electron—radicals, e.g. (1) and (2)  

Homolytic fission of an R3C—X bond is, in the gas phase, always less energy-demanding than heterolytic fission. This energetic advantage is, however, often reversed in polar solvents, because of the energy then developed—in heterolytic fission—from solvation of the developing ions. 

Reactions involving radicals occur widely in the gas phase the combustion of any organic compound is nearly always a radical reaction, and the oxidative breakdown of alkanes in internal combus- 

Another characteristic of many radical reactions is that, once initiated, they often proceed with great rapidity owing to the establishment of fast chain reactions of low energy requirement, e.g. in the halogenation of alkanes (3, cf. p. 323)  

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As in reduction reactions, two possible mechanisms exist for substitution reactions (1) electron-radical, involving the intermediate formation of radicals and their reaction with nucleophiles X ... 

Force-field methods, calculation of molecular structure and energy by, 13,1 Free radical chain processes in aliphatic systems involving an electron-transfer reaction, 23, 271 Free radicals, and their reactions at low temperature using a rotating cryostat, study of, 8. I Free radicals, identification by electron spin resonance, 1, 284... 

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