ABINITIO STUDY OF THE STRUCTURES, ROTATION INVERSION BARRIERS, FUNDAMENTAL FREQUENCIES, AND THERMODYNAMIC FUNCTIONS OF CH2CLCH2, CH3CHCL, AND CH3CCL2 RADICALS

The equilibrium geometries, rotational and inversion barriers, and harmonic vibrational spectra for beta-chloroethyl (CH2ClCH2), alpha-chloroethyl (CH3CHCl), and alpha,alpha-dichloroethyl (CH3CCl2) radicals have been determined by ab initio molecular orbital techniques using the GAUSSIAN 88 system of programs at the UHF/6-31G* level of theory. For all three radicals only one distinguishable equilibrium conformation was found on the potential energy surface. The radical centers for all three species are nonplanar. The barriers for rotation about the C-C bond and inversion of the radical center were located for each compound by analytical methods. Electron correlation energy corrections were estimated by single-point UMP2/6-311G**//6-31G* calculations. Vibrational frequencies, as well as moments of inertia for overall and internal rotation, are reported for each species. Calculated heat capacities, entropies, enthalpy, and free energy functions are tabulated as a function of temperature. Several homodesmic reactions have been studied for the purpose of obtaining theoretical heats of formation. The theoretical DELTA-H-degrees(f,298) values thus evaluated are 22.44, 18.26, and 11.75 kcal/mol for CH2ClCH2, CH3CHCl, and CH3CCl2 radicals, respectively, which are in good agreement with available experimental values. Thermochemical quantities DELTA-H-degrees(f,T), DELTA-G-degrees(f,T), and log K(f,T) for all three radicals are reported as a function of temperature.