Free Radicals by Mass Spectrometry: Xi. The Mercury Photosensitized Decomposition of C₂–c₄ Olefins

The mercury photosensitized (Hg 3 P 1 ) decomposition of olefins has been examined using a reactor coupled directly to a mass spectrometer. The primary split of ethylene has been shown to be predominantly molecular, and that of propylene mainly into an allyl radical and a hydrogen atom. With 1-butene the split is predominantly at a C–C bond giving allyl and methyl radicals, although a rupture of a C–H bond occurs as well. With 2-butene and isobutene a C–H bond is broken. It is concluded that the allyl and methallyl radicals produced have large cross sections for reaction with excited mercury atoms.