Can a C-H•••O Interaction Be a Determinant of Conformation?

Whether nonconventional hydrogen bonds, such as the C-H center dot center dot center dot O interaction, are a consequence or a determinant of conformation is a long-running and unresolved issue. Here we outline a solid-state and quantum mechanical study designed to investigate whether a C-H center dot center dot center dot O interaction can override the significant trans-planar conformational preferences of alpha-fluoroamide substituents. A profound change in dihedral angle from trans-planar((OCCF)) to cis-planar((OCCF)) observed on introducing an acceptor group for a C-H center dot center dot center dot O hydrogen bond is consistent with this interaction functioning as a determinant of conformation in certain systems. This testifies to the potential influence of the C-H center dot center dot center dot O hydrogen bond and is consistent with the assignment of this interaction as a contributor to overall conformation in both model and natural systems.