Enthalpy of formation and bond energies on unsaturated oxygenated hydrocarbons using G3MP2B3 calculation methods

Abstract

AbstractEnthalpies of unsaturated oxygenated hydrocarbons and radicals corresponding to the loss of hydrogen atoms from the parent molecules are intermediates and decomposition products in the oxidation and combustion of aromatic and polyaromatic species. Enthalpies (ΔfH0298) are calculated for a set of 27 oxygenated and nonoxygenated, unsaturated hydrocarbons and 12 radicals at the G3MP2B3 level of theory and with the commonly used B3LYP/6‐311g(d,p) density functional theory (DFT) method. Standard enthalpies of formation (ΔfH0298) are determined from the calculated enthalpy of reaction (ΔH0rxn,298) using isodesmic work reactions with reference species that have accurately known ΔfH0298 values. The deviation between G3MP2B3 and B3LYP methods is under ±0.5 kcal mol−1 for 9 species, 18 other species differs by less than ±1 kcal mol−1 , and 11 species differ by about 1.5 kcal mol−1. Under them are 11 radicals derived from the above‐oxygenated hydrocarbons that show good agreement between G3MP2B3 and B3LYP methods. G3 calculations have been performed to further validate enthalpy values, where a discrepancy of more than 2.5 kcal mol−1 exists between the G3MP3B3 and density functional results. Surprisingly the G3 calculations support the density functional calculations in these several nonagreement cases. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 633–648, 2005