DFT study on IR spectral and structural changes caused by the conversion of substituted benzophenones into ketyl radicals

The structural and spectral changes, arising from the conversion of a series of benzophenones into ketyls, are studied on the basis of standard DFT methods, employing different functionals and basis sets, without and with inclusion of solvent. Their relative predictive capabilities are evaluated by comparing the theoretically predicted and experimentally observed carbonyl frequencies. A very good agreement is achieved at combination between IEFPCM and ONIOM method with the basis functions 6-311+G(2df,p) for high layer and 6-311+G for low layer, showing the relevance of including high-order polarization functions in the basis set of high layer and solvent effect. The chosen level of theory ONIOM[B3LYP/6-311+G(2df,p)//6-311+G]-IEFPCM is applied to analyze the vibrational spectra, geometry and spin populations over the CO groups of the title species. The spin populations over the CO groups in ketyls correlate excellently with these decreases ΔνCO and prove to be dominant factor determining the frequency variation in the IR spectra.