Kinetic and spectroscopic evidence support the conclusion that chlorinated solvents such as CH2Cl2, CHCL3 and CCl4 form stable Cl●solvent complexes during free radical photochlorination reactions. Recent ab initio computations identified stable Cl●CH2Cl2 and Cl●CHCl3 complexes with binding energies determined at the G3 composite method of -3.3 kJ mol-1 and -6.6 kJ mol-1, respectively. Both complexes have Cs symmetry. A DFT study at M062X/aug-cc-pVTZ model chemistry found a stable Cl●CHCl3 complex of C1 symmetry with a binding energy of -16 kJ mol-1. We have probed the potential energy surfaces for Cl atom complexation with CH2Cl2 and CHCl3 employing several recent DFT methods including long-range corrected and double-hybrid functionals with empirical dispersion corrections (M062X, M11, ωB97X, ωB97X-D, B2PLYP, B2PLYPD and B2PLYPD3) and MP2 employing aug-cc-pVXZ (X=2-4). Two Cl atom complex geometries of Cs and C1 symmetries were obtained for each of the chlorinated solvents. MP2 optimization gave very similar geometries. Optimizations were carried out both with and without counterpoise corrections and it was observed that the effect of basis set superposition error (BSSE) on both the potential energy surface and energy was negligible with the aug-cc-pVQZ basis set. Complex stabilization energies were obtained using the supermolecule approach and all electronic energies were corrected by addition of scaled zero point vibrational energies. The DFT methods gave stabilization energies for the two complexes obtained for Cl atom interaction with CH2Cl2ranging from -14.7 to -18.2 kJ mol-1, whereas stabilization energies for the two complexes obtained from CHCl3 ranged from -10.2 to -13.3 kJ mol-1. For comparison, complex energy for the Cs symmetry chlorine atom complex with CH2Cl2 (figure 1) determined at the CCSD(T)/aug-cc-pVTZ//M11/aug-cc-pVQZ model chemistry is -17.9 kJ mol-1.

Theoretical study of chlorine atom complexation by chloro-substituted methanes: Benchmark energies and performance of DFT methods. ω

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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