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Hydrogen bonding is a special type of dipole-dipole attraction that occurs between molecules. It happens when hydrogen is directly bonded to a highly electronegative atom, such as nitrogen, oxygen, or fluorine. This creates a strong attractive force.
When hydrogen bonds form, they significantly influence the properties of a substance, such as its boiling and melting points. The reason for this is due to the energy required to break these bonds.
Ethanol and ethylene glycol are excellent examples of substances that exhibit hydrogen bonding. Ethanol contains an -OH group, making it capable of forming hydrogen bonds. Similarly, ethylene glycol has two -OH groups, allowing for even more hydrogen bonding and thus a higher boiling point.

Dipole-dipole interactions occur between polar molecules. These are molecules with an uneven distribution of charges, resulting in partial positive and negative charges.
These interactions are generally weaker than hydrogen bonds but stronger than London dispersion forces.
Acetone, mentioned in the exercise, is a great example of a molecule that experiences dipole-dipole interactions. Its carbonyl group (C=O) is highly polar, meaning acetone molecules attract each other via these dipole-dipole forces.

Boiling point is a critical property which can tell us a lot about a substance's intermolecular forces. The stronger the intermolecular forces within a substance, the higher its boiling point typically is.
Substances with hydrogen bonding, like ethylene glycol, generally have higher boiling points compared to those with only dipole-dipole interactions, such as acetone.
To determine which substance has the highest boiling point as in our exercise, we examine their intermolecular forces: more hydrogen bonding usually indicates a higher boiling point.

London dispersion forces are the weakest type of intermolecular forces. They are present in all molecules, whether they are polar or nonpolar.
These forces arise due to temporary shifts in electron density, which create transient dipoles. While individually weak, these forces can become significant in large molecules with many electrons.
In our context, while ethanol and ethylene glycol have stronger hydrogen bonds, London dispersion forces also play a role, especially in less polar substances.