Search for a strong, virtually "no-shift" hydrogen bond: a cage molecule with an exceptional OH⋅⋅⋅F interaction

Abstract

Reported herein is the synthesis of a molecule containing an unusually strong hydrogen bond between an OH donor and a covalent F acceptor, a heretofore somewhat ill-defined if not controversial interaction. This unique hydrogen bond is to a large extent a product of the tight framework of the rigid caged system. Remarkably, the interaction shows little to no perceptible shift in the OH stretch of the IR spectrum relative to appropriate nonhydrogen-bound standards in fairly non-interactive solvents. This fascinating example of what has been termed a virtual "no-shift" hydrogen bond is investigated through NMR (coupling constants, isotopic chemical shift perturbations, proton exchange rates) and IR studies which all tell a consistent story.

Keywords: NMR spectroscopy; cage molecules; fluorine; hydrogen bonds; noncovalent interactions.