Intramolecular OH···FC Hydrogen Bonding in Fluorinated Carbohydrates: GHF is a Better Hydrogen Bond Acceptor than CF2

摘要

Hydrogen bonds (H-bonds) are well-appreciated key interactions, playing a major role in stabilizing tertiary structures of peptides and nucleic acids, and being involved in molecular recognition. Still, an official definition of the hydrogen bond was only recently published by the IUPAC. Fluoroorganic compounds are widely used in materials, pharmaceuticals, and agrochemicals, but the extent to which organofluorines can act as hydrogen bond acceptor and how the proximal substituents affect this interaction is still actively researched and debated. A recent review of Schneider summarizes the current knowledge about X-H-F-C H-bonds (X = 0, N, S, and C) and describes the methods used to experimentally identify factors influencing this weak interactions. X—H···F-C H-bonds are best assigned by X-ray diffraction in the solid state, by computational methods in the gas phase, and by IR and NMR spectroscopy in the liquid phase. They prefer to be linear, with the bending of intramolecular H-bonds leading to a decrease of the stabilization (e.g. 14 kJmol~(-1) for a linear and5 kJ mol~(-1) for a bent O-H···F H-bond in a five-membered ring). The strong interest on XH···F H-bonds is evidenced by a recent IR investigation of the intramolecular OH···F H-bonding in fluorinated anancomeric cyclohexanols and by the detection of intermolecular XH—F (X = O or N) H-bonds by ~(19)F NMR spectroscopy in complexes of fluorinated agents with enzymes.