Rotational strength sign and normal modes description: A theoretical and experimental comparative study in bicyclic terpenes.

A comparative study of the Vibrational circular dichroism (VCD) patterns in three bicyclic terpenes with related molecular structures, (+)-(R)-α-pinene, (-)-(S)-β-pinene, and (-)-(S)-verbenone, is carried out. The study is done in the light of normal mode descriptions from a previous vibrational analysis. Although normal modes corresponding to identical molecular moieties shown the same description, rotational strength does not follow the Cahn-Ingold-Prelog descriptor-related sign in some cases, i.e., they do not present opposite signs depending on stereochemical description of the molecule.