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Reactions of the ethyl radical. II. Addition to unsaturated hydrocarbons

1958; Royal Society; Volume: 244; Issue: 1238 Linguagem: Inglês

10.1098/rspa.1958.0043

2053-9169

D. G. L. James, E. W. R. Steacie,

Free Radicals and Antioxidants

The kinetic study of the addition of the ethyl radical to the multiple bond has revealed the effect of various structural factors upon molecular reactivity. Hydrocarbons were selected as representative of the classes: 1-alkyne, 1-alkene and 2-methyl 1-alkene. Values for the energy of activation ( E 7 ‒ ½ E 2 ) are distinct at 8·8 ± 0·4, 7·0 ± 0·2 and 5·7 ± 0·9 kcal mole -1 respec­tively for these classes. The value of the frequency factor is sensitive to any structural feature able to restrict the access of the ethyl radical to the double bond. The absolute value for the addition rate constant for 1-heptene is k 7 = 3·2 × 10 -13 exp (‒ 8000 ± 700)/ RT cm 3 mol. -1 s -1 . A quantitative explanation is proposed for the failure of radical catalysts to polymerize 1-heptene or 1-heptyne. A number of physical models for the addition reaction are examined in relation to the results of this paper.