Formation of Substituted Alkyls as Precursors of Peroxy Radicals with a Rapid H-Shift in the Atmosphere.

Long straight-chain alkyl peroxy (ROO) radicals substituted with C═C and oxo functional groups are expected to undergo a rapid hydrogen shift (H-shift), which is a critical step in the atmospheric autoxidation mechanism. The existence of a weak tertiary C-H bond plays a key role in the rapid H-shift. Here, the reaction kinetics between OH and two typical long straight-chain functionalized volatile organic compounds, 3-methyl-1-hexene (3-MH) and 2-methylpentanal (2-MP), was theoretically investigated to reveal the fate of the weak C-H bond. The results indicate that the most favored reaction pathways are direct consumption (H-abstraction of 2-MP) and indirect destruction (addition of OH to 3-MH) of the "weak" tertiary C-H bond. The yields of abstraction pathways producing precursors of ROO radicals that undergo rapid H-shifts are computed to be less than 10% for both 3-MH + OH and 2-MP + OH reactions.