What Are Examples of Hydrogen Bonding?

Hydrogen bonds occur when a hydrogen atom undergoes dipole-dipole attraction to an electronegative atom. Usually, hydrogen bonds occur between hydrogen and fluorine, oxygen, or nitrogen. Sometimes the bonding is intramolecular, or between atoms of a molecule, rather than between atoms of separate molecules (intermolecular). 

Examples of Hydrogen Bonds

Here is a list of molecules that exhibit hydrogen bonding:

• water (H₂O): Water is an excellent example of hydrogen bonding. The bond is between the hydrogen of one water molecule and the oxygen atoms of another water molecule, not between the two hydrogen atoms (a common misconception). How this works is that the polar nature of the water molecule means each hydrogen atom experiences attraction to both the oxygen it's bound to and to the non-hydrogen side of the oxygen atoms of other water molecules. Hydrogen bonding in water results in the crystal structure of ice, making it less dense than water and able to float.
• chloroform (CHCl₃): Hydrogen bonding occurs between hydrogen of one molecule and carbon of another molecule.
• ammonia (NH₃): Hydrogen bonds form between hydrogen of one molecule and nitrogen of another. In the case of ammonia, the bond that forms is very weak because each nitrogen has one lone electron pair. This type of hydrogen bonding with nitrogen also occurs in methylamine.
• acetylacetone (C₅H₈O₂): Intramolecular hydrogen bonding occurs between hydrogen and oxygen.
• DNA: Hydrogen bonds form between base pairs. This gives DNA its double helix shape and makes replication of the strands possible, as they "unzip" along the hydrogen bonds.
• nylon: Hydrogen bonds are found between the repeating units of the polymer.
• hydrofluoric acid (HF): Hydrofluoric acid forms what is called a symmetric hydrogen bond, which is stronger than the regular hydrogen bond. This type of bond also forms in formic acid.
• proteins: Hydrogen bonds result in protein folding, which helps the molecule maintain stability and assume a functional configuration.
• polymers: Polymers that contain carbonyl or amide groups can form hydrogen bonds. Examples include urea and polyurethane and the natural polymer cellulose. Hydrogen bonding in these molecules increases their tensile strength and melting point.
• alcohol: Ethanol and other alcohols contain hydrogen bonds between hydrogen and oxygen.