Mechanisms of formation of vinoxy radicals in the reaction of O((3)p) withterminal alkenes

When an O(P-3) atom reacts with a terminal alkene, RCH=CH2, a vinoxy radica l can be produced by one of two mechanisms: (a) attachment of the oxygen at om to C1 followed by migration of a hydrogen atom from C1 to C2 and then re lease of the radical R, or (b) attachment of the oxygen atom to C2 followed or accompanied by release of the radical R. The hot band B <-- X spectra o f partially deuterated vinoxys allow one to distinguish between these two p ossibilities. The general result is that vinoxy is produced in comparable a mounts by the two mechanisms. In the reaction of O(P-3) atoms with ethylene , one of the product channels is a vinoxy and a hydrogen atom. A hydrogen a tom can be directly released from the carbon atom to which the oxygen is at tached or it can migrate to the other carbon forming a hot acetaldehyde. Th e latter then dissociates to form methyl and formyl radicals (mainly) or a hydrogen atom and a vinoxy radical. The hot band spectra of vinoxys from th e reaction of O(P-3) with CHD=CHD and CH2=CD2 show that while both processe s occur, the majority of the hydrogen atoms are released directly rather th an indirectly. Fast hydrogen atoms produced by photodissociation of H2S wer e shown to abstract a hydrogen atom from the methyl group of acetaldehyde y ielding a hydrogen molecule and vinoxy. The vinoxy is vibrationally very co ld despite the large available energy.