Reactions of Certain Radicals

Consider now the reactions of individual radicals, particularly of hydroxyl. Hydroxyl reacts with hydrogen according to OH Hg HgO + H and with carbon monoxide according to OH + CO COg + H. The reactions of hydroxyl with several hydrocarbons have also been studied. In all these reactions the dominant process is 

The rate constants of reactions between hydroxyl and simple alkanes 

Hydrogen-atom abstraction is also the basic step in the reactions of hydrocarbon radicals with hydrogen-containing molecules. 

Alkyl radicals readily add to olefin molecules and other unsaturated (in particular aromatic) ones. Experimental evidence shows that the activation energy for the addition of an alkyl radical to an olefin molecule is up to 30 kJ. 

Complex hydrocarbon radicals tend to unimolecular decay as well. This is evident from experimental results on the thermal decomposition of hydrocarbons and also from the low energies for C—C and C—H bond splitting in radicals (known from thermochemical data) which makes thermal decay of a radical very probable, even at relatively low temperatures. 

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Polar effects also appear to exist in the addition reactions of certain radicals to substituted ethylenes. It is clear from Table II that for electronegative radicals like difluoroamino or hydroxy and to a lesser extent trifluoromethyl radical and hydrogen atom, substitution with donor groups like methyl increases the rate of addition. Substitution with electronegative atoms like fluorine or chlorine has the effect of slowing the rate of addition by hydroxy or trifluoromethyl radicals but the rate of addition of methyl radicals is increased. 

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