Thermochemical Properties, Rotation Barriers, and Group Additivity for Unsaturated Oxygenated Hydrocarbons and Radicals Resulting from Reaction of Vinyl and Phenyl Radical Systems with O2
journal contributionposted on 17.03.2005, 00:00 by Nadia Sebbar, Henning Bockhorn, Joseph W. Bozzelli
Oxidation of unsaturated and aromatic hydrocarbons in atmospheric and combustion processes results in formation of linear and cyclic unsaturated, oxygenated-hydrocarbon intermediates. The thermochemical parameters , , and Cpf298(T) for these intermediates are needed to understand their stability and reaction paths in further oxidation. These properties are not available for a majority of these unsaturated oxy-hydrocarbons and their corresponding radicals, even via group additivity methods. Enthalpy, entropy, and heat capacity of a series of 40 oxygenated and non-oxygenated molecules, or radicals corresponding to hydrogen atom loss from the parent stable molecules are determined in this study. Enthalpy ( in kcal mol-1) is derived from the density function calculations at the B3LYP/6-311g(d,p) calculated enthalpy of reaction ( ) and by use of isodesmic (work) reactions. Estimation of error in enthalpy ( ), from use of computational chemistry coupled with work reactions analysis, is presented using comparisons between the calculated and literature enthalpies of reaction. Entropies ( ) and heat capacities (Cpf298(T)) were calculated using the B3LYP/6-311G(d,p) determined frequencies and geometries. Potential barriers for internal rotors in each molecule were determined and used (in place of torsion frequencies) to calculate contributions to S and Cp(T) from the hindered rotors. Twenty-six groups for use in group additivity (GA) are also developed.