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| - Thermodynamic Properties and Kinetic Parameters for Cyclic Ether Formation fromHydroperoxyalkyl Radicals
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| - Rates and thermochemistry for the cyclization of various hydroperoxyalkyl radicals •QOOH with up to sixcarbons to form cyclic ethers plus OH are computed using complete-basis-set (CBS) and density-functionaltheory (DFT) methods. Effects of mono- and dialkyl substitution α to the OOH group and β to the radicalcenter were also studied. Many quantum chemical methods have difficulty accurately predicting peroxideenergetics and particular problems with the transition state calculations. The popular B3LYP methodunderestimates many barrier heights as well as O−O bond strengths by up to 8 kcal/mol. The relatedBH&HLYP method appears to give more accurate barrier heights predictions than B3LYP, but itsthermochemistry is inaccurate and it overestimates the heats of reaction by up to 5 kcal/mol. For the transitionstates, there are subtle problems even with high-level CBS methods. But from the many calculations, a consistentpicture emerges and is compared with the limited existing experimental data. Improved hydrogen-bondincrement (HBI) values for β-hydroperoxyalkyl radicals and ring strain corrections (RSC) for cyclic etherswith 3-, 4-, and 5-membered rings are derived. Generalized rate estimation rules for the decomposition ofalkyl-substituted •QOOH to form cyclic ethers are presented based on the observed Evans−Polanyi correlationbetween the computed barrier height and the reaction exothermicity. Issues that must be resolved beforethese results can be usefully applied in ignition and partial oxidation models are outlined.
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