Branching ratios peroxy radical reactions

The branching ratios shown are estimates based on reference 65. The further oxidation of each of the isomers is similar, so only the first isomer will be examined in detail. In continental areas with at least tens of pptrv s of NO, the peroxy radical produced in the first step will react with NO. This reaction can result in either oxidation of NO to N02 or production of an organic nitrate (bold type indicates organic nitrates that are assumed to be stable) ... 

Pathway (b) is always the minor channel. For small hydrocarbon peroxy radicals the branching ratio kjk increases from <0.014 for R = C2H5 to approximately 0.2 for n-hexane. As the hydrocarbon grows further, a branching ratio of kf,/k = 0.4 is approached (e.g., for n-octane) [12]. With respect to the HCFC-based peroxy radical plus NO reactions, there have been no reports of either a pressure dependence to the reaction or of observations of alkyl nitrate formation. Most of the studies base the conclusion that channel (b) is insignificant on the observation that the NO2 produced approximately equals the initial peroxy radical concentration. 

Self-reaction rate coefficients (kj) and branching ratios (a) obtained in this laboratory for a series of peroxy radicals, are presented in Table 2, where a is defined as the fraction of the reaction proceeding via the propagating channel, i.e. ksJks ... 

Percent product distribution propanal 50.6 1.2, 2-hydroxy-butanal 7.0 0.3, l-hydroxy-butan-2-one 24.2 0.7, 1,2 dihydroxybutane 18.2 0.7. Computer assisted analysis of the product distribution showed that addition of the OH radical occurs to 26 % at the inner and to 74% at the outer position of the double bond. These reactions produced the corresponding primary and secondary hydroxy-alkylperoxy radicals. The branching ratio for the radical propagating channel of the self-reaction of the secondary peroxy radicals was determined to be issa/ iss = 0.75 0.02 28 % of the hydroxy-alkoxyl radical thus formed reacted with oxygen to produce hydroxyketone. If it is assumed that the rate coefficient for the reaction of the hydroxy-alkoxyl radical with oxygen is 8 x 10 cm molecule s the rate coefficient for the decomposition of this radical to produce propanal is 1 x 10 s V... 

---