More on hydrogen bonding interactions
Studies of hydrogen bond strength and directionality are largely based on crystal structures which can be biased by crystal packing forces. In a systematic QM study of a wide range of hydrogen bonding groups by Diogo Santos-Martins, Stefano Forli, 34 donors and 67 acceptors DOI they showed there is no correlation between the strength of the hydrogen bond and directionality.
Results demonstrate that there are very strong HB acceptors (e.g.,DMSO) with nearly isotropic interactions, and weak ones (e.g.,thioacetone) with a sharp directional profile. Similarly, groups can have comparable directional propensity, but be very distant in the strength spectrum (e.g., thioacetone and pyridine).
This work also includes a fabulous sheet in the supplementary information giving details of interaction energies for various groups.
I've updated the molecular interactions page.