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Some observations on the kinetics and thermochemistry of the reactions of HO 2 radicals with aldehydes and ketones
Author(s) -
Benson S. W.
Publication year - 2001
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.1047
Subject(s) - thermochemistry , chemistry , hydroperoxyl , radical , kinetics , standard enthalpy of formation , transition state , alkoxy group , computational chemistry , photochemistry , organic chemistry , catalysis , alkyl , physics , quantum mechanics
Abstract The rapid, gas phase equilibrium addition of HO 2 radicals to CH 2 O to form the peroxy radical HOCH 2 OO • is in agreement with the known thermochemistry of these species. The recent study of the similar addition of HO 2 • to ketones shows no significant reaction, which is again in agreement with known thermochemistry. All these reactions are notable for significant dipole attraction between the reactants ranging from 3 to 7 kcal/mol. The thermochemistry shows that the hydroperoxyl alkoxy species, the primary possible adduct, is not favored by the free energy change for direct addition. This and the observed kinetics favor a concerted addition, H‐atom transfer, as the transition state for the reactions. Kinetic estimates for forward and reverse reactions are in good agreement with observations. A thermochemical examination of the step‐wise addition of HO 2 • to the carbonyl shows that the reaction proceeds through a concerted, cyclic transition state involving simultaneous H‐transfer, 3 + 2 cyclo‐addition of HO 2 • to the carbonyl group. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 509–512, 2001