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# Hydrogen Bonding

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 Sub Topics Hydrogen bonding is of universal importance. It is central to the understanding of the microscope structures and functions in many complex systems, for example hydrogen bonded water or alcohol networks, organic compounds in solution crystal engineering, proteins and DNA building blocks of life.  Hydrogen bonding can be either an important or intramolecular phenomenon. An intermolecular H-bond is one for which the donor and acceptor units are found in two different molecules, for an intramolecular H-bond they are in the same molecule.

## Strength of Hydrogen Bond

The hydrogen bond strength depends on its length and angle and hence, it has directionality. Nevertheless small derivations from linearity in the bond angle have marginal effect on H-bond strength. The dependency of the same on H-bond length is very important and has been shown to decay exponentially with distance. Strengthening hydrogen bonding has particularly important effects on viscocity and diffusion as indicated by the large changes occurring in super cooled normal water.

For example, the $\alpha$-helix conformation of a polypeptide is stabilized by intra-chain H-bonding , while the $\beta$-sheet conformation is stabilized by inter-chain H-bonding. The strength of H-bond is strongly dependent on the solvent polarity; the addition of a polar solvent can decrease the H-bond strength significantly, over several orders of magnitude, because the solvent molecule can also take part in H-bonding interactions. As a result, nonpolar solvents are mostly used for the preparation of H-bonded supramolecular materials.