Hydrogen bond (H-bond) effects are known: it makes sea water iquid, joins cellulose microfibrils in trees, shapes DNA nto genes and polypeptide chains into wool, hair, muscles or enzymes. Its true nature is less known and we may still wonder why O-H...O bond energies range from less than 1 to more than 30 kcal/mol without apparent reason. This H-bond puzzle is re-examined here from its very beginning and presented as an inclusive compilation of experimental H-bond energies and geometries.
New concepts emerge from this analysis: new classes of systematically strong H-bonds (CAHBs and...