Fig. 5. Computational investigations. (A) CBS-QB3-computed free energy profile for HOO˙ formation from peroxyl radical intermediates arising in styrene autoxidation. Energy of the tunneling-enhanced 1,4-HAT TS is given by the dashed line. Methylperoxyl and methoxyl are used as models of chain-propagating alkylperoxyl and alkoxyl radicals, respectively. Transition state structures for the 1,4-HAT in the β-alkoxyalkylperoxyl radicals derived from styrene (B), norborene (C) and cyclooctene (D).