Are C−H Groups Significant Hydrogen Bonding Sites in Anion Receptors? Benzene Complexes with Cl^-, NO₃^-, and ClO₄^-

Theoretical calculations,examination of crystallographic data, and experimental binding energies suggest that even in the absence of electron-withdrawing substituents, simple arenes such as benzene form hydrogen bonds with anions that can exceed 50% of the strength of those formed by O−H and N−H groups. Thus, when present in a receptor, even moderately acidic C−H groups can significantly enhance the anion binding affinity and they should be considered as additional binding sites within the host cavity.