Mechanism and Rate Constants for the Decomposition of 1-Pentenyl Radicals
This paper is concerned with the mechanisms and rate constants for decomposition of 1-penten-3-yl , 1-penten-4-yl and 1-penten-5-yl radicals. They are formed from radical attack on the 1-pentene that is an important decomposition product of normal alkyl radicals with more than 6 carbon atoms. This work is based on related data in the literature. These involve rate constants for the reverse radical addition process under high pressure conditions, chemical activation experiments and more recent direct studies. High pressure rate constants are based on detailed balance. Energy transfer effects and the pressure dependence of the rate constants are determined through the solution of the master equation and projected to cover combustion conditions. The low barriers to these reactions make it necessary to treat these thermal reactions as open systems as in chemical activation studies. The multiple reaction channels make the nature of the pressure effects different than those usually described in standard texts. The order of stability is 1-penten-3-yl ~ 1-penten-4-yl> 1-penten-5-yl and straddle those for the n-alkyl radicals. A key feature in these reactions is the effects traceable to allylic resonance. However, the 50 kJ/mol allylic resonance energy is not fully manifested. The important unsaturated products are 1,3-butadiene, the pentadienes, allyl radicals and vinyl radicals. Results are compared with the recommendations in the literature and significant differences are noted. Extensions to larger radicals with similar structures are discussed.