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Published January 17, 2019 | Supplemental Material
Journal Article Open

Intramolecular Hydrogen Shift Chemistry of Hydroperoxy-Substituted Peroxy Radicals


Gas-phase autoxidation – the sequential regeneration of peroxy radicals (RO_2) via intramolecular hydrogen shifts (H-shifts) followed by oxygen addition – leads to the formation of organic hydroperoxides. The atmospheric fate of these peroxides remains unclear, including the potential for further H-shift chemistry. Here, we report H-shift rate coefficients for a system of RO_2 with hydroperoxide functionality produced in the OH-initiated oxidation of 2-hydroperoxy-2-methylpentane. The initial RO_2 formed in this chemistry are unable to undergo α-OOH H-shift (HOOC–H) reactions. However, these RO_2 rapidly isomerize (>100 s^(–1) at 296 K) by H-shift of the hydroperoxy hydrogen (ROO–H) to produce a hydroperoxy-substituted RO_2 with an accessible α-OOH hydrogen. First order rate coefficients for the 1,5 H-shift of the α-OOH hydrogen are measured to be ∼0.04 s^(–1) (296 K) and ∼0.1 s^(–1) (318 K), within 50% of the rate coefficients calculated using multiconformer transition state theory. Reaction of the RO_2 with NO produces alkoxy radicals which also undergo rapid isomerization via 1,6 and 1,5 H-shift of the hydroperoxy hydrogen (ROO–H) to produce RO_2 with alcohol functionality. One of these hydroxy-substituted RO_2 exhibits a 1,5 α-OH (HOC–H) H-shift, measured to be ∼0.2 s^(–1) (296 K) and ∼0.6 s^(–1) (318 K), again in agreement with the calculated rates. Thus, the rapid shift of hydroperoxy hydrogens in alkoxy and peroxy radicals enables intramolecular reactions that would otherwise be inaccessible.

Additional Information

© 2018 American Chemical Society. Received: October 5, 2018; Revised: December 10, 2018; Published: December 14, 2018. J.C.H. thanks the Camille and Henry Dreyfus postdoctoral program in Environmental Chemistry for support. We acknowledge funding from the National Science Foundation (Grant CHE-1508526), the University of Copenhagen, and the Danish Center for Scientific Computing. The authors declare no competing financial interest. The wB97X-D/aug-cc-pVTZ optimizations and frequencies and the CCSD(T)-F12a/VDZ-F12 single point energy calculations are available at https://sid.erda.dk/public/archives/4f4b98346d6b007ba44411c642b39fa1/published-archive.html.

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August 22, 2023
October 19, 2023