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 C₁₅ alkene, 1-pentadecene, was reacted with NO₃ radicals in a Teflon environmental chamber and yields of secondary organic aerosol (SOA) and particulate β-hydroxynitrates, β-carbonylnitrates, and organic peroxides (β-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 β-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 β-hydroxynitrates (0.060 and 0.005 for 1-nitrooxy-2-hydroxy­pentadecane and 1-hydroxy-2-nitrooxy­pentadecane isomers), 0.102 for β-carbonylnitrates, 0.017 for organic peroxides, 0.232 for β-nitrooxyalkoxy radical isomerization products, and 0.584 for tetradecanal and formaldehyde, the volatile C₁₄ and C₁ products of β-nitrooxyalkoxy radical decomposition. Branching ratios for decomposition and isomerization of β-nitrooxyalkoxy radicals were 0.716 and 0.284 and should be similar for other linear 1-alkenes ≥ C₆ 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.