Products and Mechanism of the Reaction of 1-Pentadecene with NO3 Radicals and the Effect of a -ONO2 Group on Alkoxy Radical Decomposition

The linear C-15 alkene, 1-pentadecene, was reacted with NO3 radicals in a Teflon environmental chamber and yields of secondary organic aerosol (SOA) and particulate beta-hydroxynitrates, beta-carbonylnitrates, and organic peroxides (beta-nitrooxyhydroperoxides + dinitrooxyperoxides) were quantified using a variety of methods. Reaction occurs almost solely by addition of NO3 to the C=C double bond and measured yields of beta-hydroxynitrate isomers indicate that 92% of addition occurs at the terminal carbon. Molar yields of reaction products determined from Measurements, a proposed reaction mechanism, and mass-balance considerations were 0.065 for beta-hydroxynitrates (0.060 and 0.005 for 1-nitrooxy-2-hydroxypentadecane and 1-hydroxy-2-nitrooxypentadecane isomers), 0.102 for beta-carbonylnitrates, 0.017 for organic peroxides, 0.232 for beta-nitrooxyalkoxy radical isomerization products, and 0.584 for tetradecanal and formaldehyde, the volatile C-14 and C-1 products of beta-nitrooxyalkoxy radical decomposition. Branching ratios for decomposition and isomerization of beta-nitrooxyalkoxy radicals were 0.716 and 0.284 and should be similar for other linear 1-alkenes >= C-6 whose alkyl chains are long enough to allow for isomerization to occur. These branching ratios have not been measured previously, and they differ significantly from those estimated using structure-activity relationships, which predict >99% isomerization. It appears that the presence of a -ONO2 group adjacent to an alkoxy radical site greatly enhances the rate of decomposition relative to isomerization, which is otherwise negligible, and that the effect is similar to that of a -OH group. The results provide insight into the effects of molecular structure on mechanisms of oxidation of volatile organic compounds and should be useful for improving structure-activity relationships that are widely used to predict the fate of these compounds in the atmosphere and for modeling SOA formation and aging.