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.