Addition of radicals to aromatic compounds

Jackson points out that, using H atom additions as a guide, radical additions to benzene will be approximately 11 kcal less exothermic than with ethylene, assuming that an extrapolation to other radicals is valid. This means that for most radicals, addition will be reversible at usual laboratory reaction temperatures of 25—100°C. Only the formation of an 

The addition of H atoms to benzene and tpluene has been investigated by a number of the same workers who studied H-atom additions to the simple olefins. The reaction with benzene and other aromatics is slower than that with ethylene, as would be expected. The greater reliability of the data obtained for additions to olefins makes the rate coefficient obtained by measuring the relative reactivity versus propene [11], and that from the more recent work on toluene [208], the preferred rate determinations. (See Table 61.) 

The reactions of trifluoromethyl radicals with a wide variety of aromatic compounds has been an active area of investigation for some time. The studies have not included determinations of the isomer distributions of the products, so that the rate coefficients quoted in the table below are actually composite ones for attack on all of the positions on the ring. A pair of rate studies for the CClFj radical are appended to the end of Table 62. 

At the end of this chapter, one may conclude that (a) an enormous amount of work has gone into obtaining these numerous rate coefficients and Arrhenius parameters, and (b) an even greater amount of work 

Addition of CF3 and CCIF2 radicals to various aromatic compounds 

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