TY - JOUR
T1 - Intramolecular Hydrogen Shift Chemistry of Hydroperoxy-Substituted Peroxy Radicals
AU - Praske, Eric
AU - Otkjær, Rasmus V.
AU - Crounse, John D.
AU - Hethcox, J. Caleb
AU - Stoltz, Brian M.
AU - Kjaergaard, Henrik G.
AU - Wennberg, Paul O.
PY - 2019/1/17
Y1 - 2019/1/17
N2 - 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.
AB - 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.
U2 - 10.1021/acs.jpca.8b09745
DO - 10.1021/acs.jpca.8b09745
M3 - Journal article
C2 - 30547575
SN - 1089-5639
VL - 123
SP - 590
EP - 600
JO - Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory
JF - Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory
IS - 2
ER -