Theoretical Study on the Gas-Phase Reactivity of Halogenated Alkylperoxyl Radicals Toward alkenes

摘要

The electrophilic additions of hydroperoxyl (HO_2~.), alkylperoxyl (RO_2~.), and halogenated alkylperoxyl radicals to ethylene were studied using the AM1 and PM3 semiempirical MO methods at the SCF/UHF level. Reactantlike transition states were predicted for the title additions. The AM1 activation enthalpies (#DELTA#H_f~*) were found to be increased in the order HO_2~. < CH_3O_2~. < C_2H_5O_2~. < i-C_3H_7O_2~..The reactivity of an alkylperoxyl radical toward ethylene was found to be increased as the degree of halogen substitution on the alkyl group increased. A good correlation was established between #DELTA#H_f~* and the Taft polar substituent constants, #sigma#~*. The Evans-Polanyi correlation between #DELTA#H_f~* and #DELTA#H_r deg was justified and the validity of the Hammond postulate was indicated. The calculated results were compared with the available experimental findings.