Hydrogen Bonding

• Hydrogen bonding is a type of dipole-dipole interaction between molecules, not a covalent bond. It is a considerably stronger force of attraction compared to dipole-dipole and London dispersion forces.
• Hydrogen bonds occur when hydrogen is bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine. This arrangement results in a large dipole moment and a positive charge on the hydrogen atom.
• The positively charged hydrogen atom is then attracted to another electronegative atom, forming a “hydrogen bond”. This can either be the same molecule (intramolecular bonding) or between different molecules (intermolecular bonding).
• This type of bonding is responsible for many of the unique properties of substances. For instance, the relatively high melting and boiling points of water are due to hydrogen bonding.
• The structure of DNA, protein folding, and the unique properties of water, including its ability to absorb large amounts of heat, are also explained by hydrogen bonding.
• Hydrogen bonding affects solubility of substances. Substances with hydrogen bonds tend to be soluble in water, a protic solvent itself capable of forming hydrogen bonds.
• Hydrogen bonding also plays a crucial role in the assembly of large biological molecules. The double helix structure of DNA and the secondary and tertiary structure of proteins greatly depend on hydrogen bond formation.
• In organic chemistry, the formation of hydrogen bonds can stabilise certain chemical species such as amines and alcohols, which can influence the products of chemical reactions.
• You’ll often encounter hydrogen bonding in discussions of physical properties such as boiling and melting points, where hydrogen-bonded substances are often anomalies due to the added intermolecular forces introduced by the bonds.
• Hydrogen bonding is also important to remember in the context of molecular polarity. A molecule can be polar overall, but still experience areas of localised polarity due to hydrogen bonding.
• It is also important to remember that although most hydrogen bonds are relatively weak compared to covalent bonds, they can become significant in large numbers. This is particularly relevant in biological systems filled with water.