REACTIONS OF ALKOXY RADICALS UNDER ATMOSPHERIC CONDITIONS - THE RELATIVE IMPORTANCE OF DECOMPOSITION VERSUS REACTION WITH O-2

The reactions of alkoxy radicals determine to a large extent the products formed during the atmospheric degradations of emitted organic compounds. Experimental data concerning the decompositions, 1,5-H shift isomerizations and reactions with O2 of several classes of alkoxy radicals are inconsistent with literature estimations of their absolute or relative rate constants. An alternative, although empirical, method for assessing the relative importance under atmospheric conditions of the reactions of alkoxy radicals with O2 versus decomposition was derived. This estimation method utilizes the differences in the heats of reaction, DELTA(DELTA-H) = (DELTA-H(decomposition) - DELTA-H(O2 reaction)), between these two reactions pathways. For DELTA(DELTA-H) less-than-or-similar-to [22 - 0.5(DELTA-H(O2 reaction))], alkoxy radical decomposition dominates over the reaction with O2 at room temperature and atmospheric pressure of air, while for DELTA(DELTA-H) greater-than-or-similar-to [25 - 0.5(DELTA-H(O2 reaction))], the O2 reaction dominates over decomposition (where the units of DELTA-H are in kcal mol-1). The utility and shortcomings of this approach are discussed. It is concluded that further studies concerning the reactions of alkoxy radicals are needed.