Both the free-radical reactions of cyanogen chloride and cyanogen with hydrocarbon substrates proceed by chain mechanisms involving intermediate imidyl radicals. In the reaction of cyanogen with 2,3-dimethylbutane the imidyl radical was found to be the chain-carrying species while in the reactions of cyanogen chloride with a variety of hydrocarbons, the imidyl intermediate undergoes a β-scission reaction producing the alkyl cyanide plus a chlorine atom which then carries the chain. The mechanism of the cyanation reaction of cyanogen chloride has been shown to proceed through a chain sequence of reactions in which each step was demonstrated to be reversible. The high selectivity observed in these cyanations was found to be due to the reversible reaction of the alkyl radicals formed with the hydrogen chloride produced in the reactions. © 1969, American Chemical Society. All rights reserved.