Theoretical investigation of the structures and properties of fluoromethyl peroxyl radicals

The equilibrium geometries, harmonic vibrational frequencies, charge distributions, spin density distributions, dipole moments, electron affinities (EAs), and CO bond dissociation energies (BDEs) of HO   • 2 , CH 3 O   • 2 , CH 2 FO   • 2 , CHF 2 O   • 2 , and CF 3 O   • 2peroxyl radicals have been calculated using ab initio molecular orbital theory and density functional theory (DFT) at the B3LYP level. The CH bond dissociation energies of the parent fluoromethanes have been calculated using the same levels of theory. Both the MP2(full) and B3LYP methods, using the 6‐31G(d,p) basis set, are found to be capable of accurately predicting the geometries of peroxyl radicals. Electron correlation accounts for ∼25% of the CH BDE of fluoromethanes and for ∼50% of the CO BDE of the corresponding peroxyl radicals. The B3LYP/6‐31G(d,p) method is found to be comparable to high ab initio levels in predicting CO BDEs of studied peroxyl radicals and CH BDEs of the parent alkanes. The progressive fluorine substitution of hydrogen atoms in methyl peroxyl radicals results in shortening of the CO bond, lengthening of the OO bond, an increase (decrease) of the spin density on the terminal (inner) oxygen, a decrease in the dipole moments, and an increase in electron affinities. Both CO BDEs and EAs of peroxyl radicals (RO   • 2 ) correlate well with Taft σ* substituent constants for the R group in peroxyl radicals. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004