Structure,Torsional Potentials,and Thermodynamic Properties #DELTA#H deg _(f298),Sdeg_(298),and C_p(T) of Chloro-Dimethyl Ethers:CH_2ClOCH_3,CHCl_2OCH_3,and CCl_3OCH_3.Density Functional and ab Initio Calculations

摘要

Thermochemical properties of oxygenated chiorocarbons are important in studies on oxidation and kinetics of chiorocarbons and in Cl initiated kinetic studies on oxidation of hydrocarbons. Enthalpy, #DELTA#H deg _(f298),entropy, S_(298), and heat capacities, C_p(T), from 300 to 1500 K are determined for three chioro-dimethyl ethers by density functional and ab initio calculation methods. Molecular structures and vibration frequencies are determined at the B3LYP/6-3 IG(d,p) density functional calculation level, with single point calculations for energy at the B3LYP/6-31l+G(3df,2p), QCISD(T)/6-31G(d,p), and CBS-Q/IB3LYP/6-31G(d,p) levels of calculation (abbreviated as CBSQ//B3~(**)).Enthalpies of formation are determined at each calculation level using the #DELTA#H_(rxn(298)) and known enthalpies of other reactants in each of seven different working reactions. Contributions to entropy and heat capacity from internal rotation of the chloro-dimethyl ethers are also determined. Evaluation of data from three isodesmic schemes, and the energies of rotational conformers, result in #DELTA#H deg_(f298) values for CH_2CIOCH_3 of -55.42+-0.91, for CHCl_2OCH_3 of -62.28+-2.10, and for CCl_3OCH_3 of -63.11 +-2.26 keal/mol at the CBS-Q//B3~(**) level. We determine enthalpy, entropy, and C_p(T) terms for the three mono-oxygenated carbon chlorine groups, where enthalpy values for use in group additivity are C/Cl/H2/O (-20.90), C/C12/H/O (-28.23), and C/C13/O(-28.69 kcal/mol),respectively.