REACTIONS INVOLVING HOT O(3P) ATOMS AND ISOMERIC 2-BUTENE

The low-pressure gas-phase investigation is reported on the reactions involving high-energy O(3P) atoms with cis- and trans-2-butene. Gas chromatographic analysis of stable hydrocarbon end products revealed a complex spectrum of compounds containing carbonyl, epoxide, and alcohol groups. The large distribution of alcohol products was a distinct feature in these hot atom systems, indicating that OH radical formation was important. These analyses revealed differences in the internal energy levels of the reaction intermediates formed through the greater pressure dependence exhibited by the degree of stereospecific addition of oxygen atoms to trans-butene then reaction with cis-butene and through the greater degree of internal rearrangement and carbon-carbon bond scission exhibited by the trans intermediate. Direct measurements using on-line mass spectrometry also revealed that CO product signals were 14.6 times higher from reactions with cis-butene than with trans-butene, indicating greater reactivity of the cis pi-bond toward oxygen atom attack. Similarly, these direct analyses revealed that OH product signals were 1.7 times higher from reactions with cis-butene, suggesting that in addition to direct H abstraction an indirect pathway involving mutual interaction with the substrate's pi-bond may have contributed, in part, to those OH products observed in then studies. Kinetic energy moderator studies supported this hypothesis through the different moderator dependencies exhibited by the OH product signals seen to arise from high-energy oxygen atom reactions with the two stereoisomers.