Competitive Unimolecular Decomposition in Chemically Activated Radical Systems. Isopropyl Radical Rupture

摘要

The competitive unimolecular decomposition of vibrationally excited 5hyphen;methylhyphen;hexylhyphen;3middot; (5MH3middot;*) and 3,4hyphen;dimethylhyphen;pentylhyphen;2middot; (34DMP2middot;*) radicals was studied in chemical activation systems in which H atoms were added to suitable olefins. The relative rate of isopropyl versus methylhyphen;radical rupture from each radical yieldsD0deg;lpar;iPrndash;Hrpar;thinsp;equals;thinsp;92.8kcal moleminus;1. Absolute rates of decomposition of 5MH3middot;*, 2MH3middot;*, and 34DMP2middot;* are compared to values obtained from the theoretical model and show good agreement The reactions of isopropyl radicals with 5MH3middot;, 2MH3middot;, and 34DMP2middot; radicals are discussed briefly; disproportionationhyphen;recombination ratios are obtained and compare favorably with values calculated according to an empirical prescription given previously. The measurement of the relative rates of decomposition of 5MH3middot;* and of 2MH3middot;* in the pseudocompetitive reaction system, Hplus;transhyphen;2hyphen;methylhexenehyphen;3, provides a relation between the energetics of the 5MH3middot; radical and the 2MH3middot; radical and supportsD0deg;lpar;5MH3middot;ndash;Hrpar;thinsp;equals;thinsp;D0deg;lpar;2MH3middot;ndash;Hrpar;. A summary of bond dissociation energies determined by the present method is given.