The potential energy surfaces for the reaction of furanyl and oxazolyl radi
cals with O-2 have been examined using the B3LYP method. The initial produc
tion of the arylperoxy radical followed by either simple decomposition or r
earrangement to yield several intermediates (aryloxy, dioxiranylaryl, or di
oxetanylaryl radicals) has been explored. Transition state structures for m
ost of the steps are presented as well as relative free energies over a ran
ge of temperatures from 298 to 2000 K. The energetics of the analogous inte
rmediates for the reaction of O-2 and other five-membered heterocyclic radi
cals derived from pyrrole and thiophene are also provided. The loss of an O
atom is generally the most accessible and energetically favored pathway of
decomposition at all temperatures. Dioxiranyl formation is favored over O-
2 loss at temperatures less than or equal to 500 K and favored in the same
temperature range over O atom loss in several cases. Dioxetanyl formation i
ncurs the greatest barrier to formation, and direct routes are not availabl
e in every molecule surveyed. However, in some cases the dioxetane radicals
transform rapidly into very stable species.