Transition State Geometry and a Polar Effect in the Reactions of Peroxy Radicals with Oxygen-Containing Compounds |
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Authors: | Denisova T G Denisov E T |
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Institution: | (1) Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432, Russia |
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Abstract: | The reactions of structurally different peroxy radicals with the C–H bonds of oxygen-containing compounds (ketones, aldehydes, ethers, and esters) were analyzed in terms of a parabolic model. The enthalpies of these reactions and the activation energies of equienthalpic reactions of peroxy radicals with hydrocarbons were calculated, and the contribution of the polar interaction E
to the activation energy was evaluated. The geometry parameters of the transition state were calculated with the use of an algorithm developed based on quantum-chemical calculations in combination with the intersecting parabolas method. It was found that the polar interaction resulted in a change in the configuration of the C···H···O reaction center in the transition state from linear to angular. A different angle (C···H···O) from 180° appeared in this case. The following linear correlation between E
(kJ/mol) and cos (180° – ) was obeyed: cos (180° – ) = 1 + 6.76 × 10–3E
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