REACTIONS OF THE ETHYL RADICAL: V ADDITION TO THE MONOMETHYL ACRYLONITRILES

Abstract

The Arrhenius parameters have been measured for the addition of the ethyl radical to methacrylonitrile and to the cis and trans isomers of crotononitrile. The energy of activation for each of these derivatives is significantly greater than for acrylonitrile. There is no significant variation among the values of the energy of activation for the monomethyl acrylonitriles, so that the introduction of a methyl group into the acrylonitrile molecule appears to raise the energy of activation by an amount which is insensitive to the position of the group. The pre-exponential factor is significantly smaller for each of the crotononitrile isomers than for methacrylonitrile; the partial shielding of the β-carbon atom of crotononitrile is thus expressed by a steric factor rather than by an energy term. The cis-trans isomerization of crotononitrile is photosensitized by diethyl ketone illuminated by o 3 130 Å radiation in both the liquid and gaseous phases; a mechanism of triplet state energy transfer is proposed for the process.