Nucleophilic character of alkyl radicals. 18. Absolute rate constants for the addition of primary alkyl radicals to conjugated olefins and 1,4-benzoquinone

The rate constants for the addition of the 5-hexenyl radical to styrene, α-methylstyrene, butadiene, acrylic monomers, methyl vinyl ketone, and 1,4-benzoquinone were measured from 16 to 69°C. The importance of polar effects, due to the nucleophilic character of the alkyl radical in olefin addition, is emphasized. The inhibition of chain processes by quinone is discussed in terms of the high rate constant (2.0 × 10 7 L mol -1 s -1 at 69°C) of the alkyl radical addition to 1,4-benzoquinone.