THE POLAR EFFECT IN THE REACTIONS OF PEROXY-RADICALS WITH ETHERS, ESTERS, AND ACIDS

A set of experimental data (rate constants and activation energies) for reactions of peroxy radicals with ethers, esters, and acids is analyzed in terms of the parabolic model of the transition state. The contribution of the polar interaction to the activation energy of this reaction is measured. In most cases, the polar interaction causes an increase in the activation energy of RO2. reaction with the C-H bond of an ether. The values of DELTAE (kJ/mol) reflecting the polar effect are as follows (the group attacked is given in brackets): 3.4 (RCH2O-), 6.3 (R1R2CHO-), 6.1 (C6H5RCHO-), 1.8 [(RO)2CH2], 6.2 [(RO)2CHCH3], 8.7 [CH3OC(O)-], 8.9 (RCH2OC(O)], 4.5 (C6H5CH2OC(O)], 7.9 [RCH2C(O)OH], 10.6 [(CH3)2CHC(O)OH], and 2.7 (CH3)2CHOR. In contrast, for some structural fragments, a decrease in the activation energy is observed; the values of -DELTAE (kJ/mol) are as follows: 3.8 (cyclo-CH2OCH2-), 3.4 (cyclo-RCHOCH2-), 2.4 (cyclo-OCH2O-), and 2.7 [RCH2C(O)OR']. A multidipole interaction was observed to affect the activation energy of the reaction between RO2' radicals formed from esters and esters themselves.