Structure, torsional potentials, and thermodynamic properties Delta H degrees(f298), S degrees(298), and C-p(T) of chloro-dimethyl ethers: CH2ClOCH3,CHCl2OCH3, and CCl3OCH3. Density functional and ab initio calculations

Thermochemical properties of oxygenated chlorocarbons are important in stud ies on oxidation and kinetics of chlorocarbons and in Cl initiated kinetic studies on oxidation of hydrocarbons. Enthalpy, DeltaH degrees (f98), entro py, S-298, and heat capacities, C-p(T), from 300 to 1500 K are determined f or three chloro-dimethyl ethers by density functional and ab initio calcula tion methods. Molecular structures and vibration frequencies are determined at the B3LYP/6-31G(d,p) density functional calculation level, with single point calculations for energy at the B3LYP/6-311+G(3df,2p), QCISD(T)/6-31G( d,p), and CBS-Q//B3LYP/6-31G(d,p) levels of calculation (abbreviated as CBS Q//B3**). Enthalpies of formation are determined at each calculation level using the DeltaH(rxn(298)) and known enthalpies of other reactants in each of seven different working reactions. Contributions to entropy and heat cap acity from internal rotation of the chloro-dimethyl ethers are also determi ned. Evaluation of data from three isodesmic schemes, and the energies of r otational conformers, result in DeltaH degrees (f298) values for CH2ClOCH3 of -55.42 +/- 0.91, for CHCl2OCH3 of -62.28 +/- 2.10, and for CCl3OCH3 of - 63.11 +/- 2.26 kcal/mol at the CBS-Q//B3** level. We determine enthalpy, en tropy, and C-p(T) terms for the three mono-oxygenated carbon chlorine group s, where enthalpy values for use in group additivity are C/Cl/H2/O (-20.90) , C/Cl2/H/O (-28.23), and C/Cl3/O (-28.69 kcal/mol), respectively.