Ab initio and DFT investigation of the structures and properties of chloromethyl and chlorofluoromethyl peroxyl radicals

Ab initio and Density Functional Theory (DFT) calculations were performed to determine the equilibrium geometries, charge distributions, spin density distributions, dipole moments, electron affinities (EAs), and C–O bond dissociation energies (BDEs) of CH₂ClO₂^? CHCl₂O₂^?, CCl₃O₂^?, CF₂ClO₂^?, CFCl₂O₂^?, and CHFClO₂^? peroxyl radicals. The C–H BDEs of the parent methanes were calculated using the same levels of theories. Both MP2(full) and B3LYP methods, using the 6‐31G(d,p) basis set, were found to be capable of accurately predicting the geometries of peroxyl radicals. The B3LYP/6‐31G(d,p) method was found to be comparable to high ab initio levels in predicting C–O BDEs of studied peroxyl radicals and C–H BDEs of the parent alkanes. The progressive chlorine substitution of hydrogen atoms in methyl peroxyl radicals results in an increase (decrease) of the spin density on the terminal (inner) oxygen, a decrease in dipole moments, and an increase in electron affinities. The substitution of fluorine by chlorine in the series CF₃O₂^? – CCl₃O₂^? was found to lengthen (destabilize) the C–O bonds. Both C–O BDEs and EAs of peroxyl radicals (RO₂^?) were found to correlate well with Taft σ* substituent constants for the R groups. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005