Intermolecular Aliphatic C–F···H–C Interaction in the Presence of “Stronger” Hydrogen Bond Acceptors: Crystallographic, Computational, and IR Studies

An unprecedented intermolecular aliphatic C–F···H–C interaction was observed in the X-ray crystal structure of a fluorinated triterpenoid. Despite the notion of fluorine being a poor acceptor, computational and IR studies revealed this interaction to be a weak to moderate hydrogen bond with a C–H stretch vibration frequency blue-shifted by 14 cm^–1 and d(F–H) = 2.13 Å. In addition, the aliphatic C–F bond is the preferred acceptor in the presence of multiple, traditionally stronger oxygen-based hydrogen bond acceptors.