Electronic circular dichroism of chiral alkenes: B3LYP and CAM-B3LYP calculations.

Time-dependent density functional theory (TDDFT) calculations of electronic circular dichroism (ECD) are widely used to determine absolute configurations (ACs) of chiral molecules. Two very popular DFT exchange-correlation functionals, one hybrid (B3LYP) and one long-range corrected (CAM-B3LYP), along with a hierarchical sequence of basis sets were investigated, and the ECD spectra predicted for eight alkenes and compared to gas-phase experimental spectra. Little variation in predicted ECD spectra was found with the basis set size enlargement, but the sensitivity to the functional is greater. Good agreement was obtained only with the CAM-B3LYP functional, leading to the conclusion that TDDFT calculations of ECD spectra can routinely provide reliable ACs if and only if an appropriate functional is used. For camphene, twistene, syn-(E)-bisfenchylidene, and phyllocladene, solvent effects were estimated.