Theoretical study on the gas-phase reactivity of halogenated alkylperoxyl radicals toward alkenes

The electrophilic additions of hydroperoxyl (HO2.), alkylperoxyl (RO2.), an d halogenated alkylperoxyl radicals to ethylene were studied using the AM1 and PM3 semiempirical MO methods at the SCF/UHF level. Reactantlike transit ion states were predicted for the title additions. The AM1 activation entha lpies (Delta H-f*)were found to be increased in the order HO2. < CH3O2. < C 2H5O2. < i-C3H7O2.. The reactivity of an alkylperoxyl radical toward ethyle ne was found to be increased as the degree of halogen substitution on the a lkyl group increased. A good correlation was established between Delta H-f* and the Taft polar substituent constants, sigma*. The Evans-Polanyi correl ation between Delta H-f* and Delta H(r)degrees was justified and the validi ty of the Hammond postulate was indicated. The calculated results were comp ared with the available experimental findings. (C) 1999 John Wiley & Sons, Inc.