Dipole-dipole interaction

Dipole-Dipole Interaction

Dipole-dipole interaction is a type of intermolecular force that occurs between molecules that possess permanent dipole moments. This interaction is one of the several mechanisms by which molecules adhere to one another in condensed phases. Unlike ionic bonds or covalent bonds, dipole-dipole interactions are comparatively weaker and are significant only when molecules are close together.

Overview

A dipole exists in a molecule when there is a separation of charge due to the unequal sharing of electrons in a chemical bond. Molecules with permanent dipoles have a positive end and a negative end, resulting from the uneven distribution of electrons. Dipole-dipole interactions arise when the positive end of one molecule is attracted to the negative end of another molecule. The strength of this interaction depends on the magnitude of the dipole moment and the distance between the molecules.

Types of Dipole-Dipole Interactions

There are several types of dipole-dipole interactions, including:

• Keesom forces: These occur between polar molecules that are stationary and oriented such that their dipoles align oppositely.
• Debye forces: These involve an interaction between a polar molecule and an induced dipole in a neighboring molecule.
• London dispersion forces: Although not strictly a dipole-dipole interaction, they are often discussed in conjunction due to their relevance in nonpolar molecules. These forces are due to temporary dipoles induced in molecules.

Importance of Dipole-Dipole Interactions

Dipole-dipole interactions play a crucial role in determining the physical properties of substances. For example, they are partly responsible for the higher boiling points of polar substances compared to nonpolar substances with similar molar masses. In biology, dipole-dipole interactions are essential for the structure and function of biomolecules, such as proteins and nucleic acids.

Examples

A classic example of a molecule with a strong dipole-dipole interaction is water (H2O). The oxygen atom has a higher electronegativity than the hydrogen atoms, creating a significant dipole moment. This interaction is responsible for many of water's unique properties, such as its high boiling point relative to its molecular weight.

See Also

• Hydrogen bond
• Van der Waals force
• Molecular polarity
• Intermolecular force