Conditions
A hydrogen bonded to a highly electronegative atom carries a large partial positive charge. When it is attracted to a lone pair on a nearby F, O or N, a hydrogen bond forms. IUPAC issued a broader definition in 2011.
Strength
Much weaker than covalent bonds but stronger than van der Waals forces, roughly 4-40 kJ/mol.
Water's unusual properties
- High boiling point compared with H2S of similar mass
- Ice floats: hydrogen bonds lock ice into an open hexagonal lattice less dense than liquid water
- High heat capacity and surface tension
Biomolecules
- DNA: A-T pairs share two hydrogen bonds and G-C pairs three.
- Proteins: they stabilize alpha helices and beta sheets.
References
- Pauling, L. (1960). The Nature of the Chemical Bond (3rd ed.). Cornell University Press.
- Arunan, E., Desiraju, G. R., Klein, R. A., et al. (2011). Definition of the hydrogen bond (IUPAC Recommendations 2011). Pure and Applied Chemistry, 83(8), 1637-1641.
- Jeffrey, G. A. (1997). An Introduction to Hydrogen Bonding. Oxford University Press.
- Watson, J. D., & Crick, F. H. C. (1953). Molecular structure of nucleic acids. Nature, 171, 737-738.