Reactions with Carbon-Hydrogen Bonds

For halocarbons that contain a carbon-hydrogen bond, reaction with tropospheric OH becomes important and their atmospheric lifetimes become dependent on the relative rates of the OH-halocar-bon reaction and the global concentration and distribution of OH. Compovmds for which OH reaction is the predominant sink include HCFCs, HFCs, CH3CCI3, CH3CI, and CH3Br. 

The occurrence of a hydrogen isotope effect in an electrophilic substitution will certainly render nugatory any attempt to relate the reactivity of the electrophile with the effects of substituents. Such a situation occurs in mercuration in which the large isotope effect = 6) has been attributed to the weakness of the carbon-mercury bond relative to the carbon-hydrogen bond. The following scheme has been formulated for the reaction, and the occurrence of the isotope effect indicates that the magnitudes of A j and are comparable ... 

The reaction rate of molecular oxygen with alkyl radicals to form peroxy radicals (eq. 5) is much higher than the reaction rate of peroxy radicals with a hydrogen atom of the substrate (eq. 6). The rate of the latter depends on the dissociation energies (Table 1) and the steric accessibiUty of the various carbon—hydrogen bonds it is an important factor in determining oxidative stabiUty. 

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