The nature of hydrogen bonds is an intriguing question. According to this post, hydrogen bonds are made primarily of electrostatic force with a small contribution of electron transfer to the antibonding orbital. This leaves some ambiguities. For example, fluorine is generally a poor hydrogen bond acceptor despite its high electronegativity. One explanation is that while C-F bonds are more polar than C-O and C-N bonds, because fluorine forms only one covalent bond, the partial charge of fluorine is generally smaller than oxygen and nitrogen. Alternatively, because fluorine is the most electronegative element, fluorine has an extremely low polarizability which makes it difficult to pull out the lone pairs.
So I came up with an interesting question whether we can design an experiment to separate them. For example, we can make many dipoles standing side by side, which can prevent the leaking of electric field like a parallel plate capacitor. This can be done with diamonds. We can prepare a highly polished <111> face of diamond crystals, and have every exposed carbon atom bind with a fluorine atom. This allows fluorine atoms to form a dense triangular array with a lattice constant of only 252 pm. Because the vdW radius of fluorine is 147 pm, these fluorine atoms can fill up the gaps between them and form a nearly perfectly planar surface. We can also make a triangular array of nitrogen atoms by replacing each CF moiety with a nitrogen atom. Because nitrogen is only slightly bigger (155 pm), the geometry won’t be much different. The efficiency of hydrogen bonding can be determined by the contact angle of water. Because the surface is nearly perfectly planar, the electrostatic contribution can be kept as small as possible.
