What is hydrogen bonding?

Hydrogen bonding is a kind of intermolecular force, which is a kind of force between permanent dipoles. Hydrogen bonding occurs between a hydrogen atom that has been bonded with other atoms with valence bond of * * * and another atom (X-H…Y). Usually, the atoms (X, Y) on both sides of the hydrogen atom with hydrogen bonding are atoms with strong electronegativity.

hydrogen bonds can be intermolecular or intramolecular. Its bond energy is about 2kJ/mol at most, generally 5-3kJ/mol, which is smaller than that of ordinary valence bonds, ionic bonds and metal bonds, but stronger than electrostatic attraction. Hydrogen bonding is particularly important for biopolymers, which is part of the reason why the secondary, tertiary and quaternary structures of protein and nucleic acids are stable.

Extended information

Influence of hydrogen bond

1. The very great solubility of ammonia in water is related to its hydrogen bond with water molecules.

2. Glycerol, anhydrous phosphoric acid and sulfuric acid have great viscosity.

3. There are intramolecular hydrogen bonds in o-nitrophenol, so its melting point is lower than that of m-nitrophenol and p-nitrophenol.

4. Water molecules in ice occupy a low space in the crystal structure of ice, so the density of ice is small, even less than that of water.

5. Every water molecule in the ice participates in the formation of four O-H…O hydrogen bonds along the tetrahedral direction. The heat of fusion of ice is 5.kJ/mol, while the energy of hydrogen bond in ice is 18.8kJ/mol, so there are still a lot of hydrogen bonds in the newly melted water. At 4℃, the trend of water-hydrogen bond breaking (density increasing) and heated molecular spacing increasing (density decreasing) are equal, so the water density is the highest at 4℃. This temperature is very important for aquatic organisms, which ensures that aquatic organisms will not die because of water freezing in winter.

6. The formation of intramolecular hydrogen bonds often enhances the acidity. For example, the Ka of benzoic acid is 96.2× 1? And the ka of o-hydroxybenzoic acid is 9.9× 1-? 2,6- dihydroxy benzoic acid can form two hydrogen bonds in the molecule, and its Ka = 5× 1 ~ 9. The reason is that the formation of intramolecular hydrogen bonds promotes the dissociation of hydrogen.

7. There is an ice-like skeleton constructed by hydrogen bonds in crystalline hydrate, which can be filled with small molecules or ions. See methane gas-water mixture.

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