Circular Dichroism and TDDFT Investigation of Chiral Fluorinated Aryl Benzyl Sulfoxides

A series of ten chiral aryl benzyl sulfoxides with perfluorinated aryl or benzyl rings, obtained by enantioselective oxidation of sulfides, has been investigated by means of electronic circular dichroism (ECD) spectroscopy and time-dependent DFT (TDDFT) calculations. The (per)fluorination of the aromatic rings has a large impact on the conformer population, the molecular orbitals shape, and the character of electronic transitions. In this series, the transition responsible for the "sulfoxide primary" CD band has a large charge transfer (CT) character, as demonstrated by the CT metric index Γ_NTO. As a consequence, global DFT hybrids such as B3LYP are largely inaccurate in the prediction of excited states; nevertheless, a correct simulation of CD spectra may be achieved by using range-separated functionals such as CAM-B3LYP. The use of the empirical Mislow's rule for assigning the absolute configuration is strongly discouraged for this class of compounds. A series of ten chiral aryl benzyl sulfoxides with perfluorinated aromatic rings has been investigated by means of electronic circular dichroism and time-dependent DFT calculations. The perfluorination has a large impact on the molecular orbitals and electronic transitions. Range-separated functionals perform much better than global hybrids in the prediction of the ECD spectra.