What are the intermolecular forces that ethylene glycol exhibit(s)?
Dispersion and dipole-dipole
Dispersion and H-bonding
Dispersion, dipole-dipole, and H-bonding
dipole-dipole and H-bonding
The Correct Answer and Explanation is:
Correct Answer: Dispersion, dipole-dipole, and H-bonding
Explanation (300+ words):
Ethylene glycol (chemical formula: C₂H₆O₂, also known as HO–CH₂–CH₂–OH) is a small organic molecule with two hydroxyl (–OH) groups. Its structure plays a significant role in the types of intermolecular forces (IMFs) it can exhibit. Understanding these forces helps explain its physical properties, such as high boiling point and solubility in water.
1. Dispersion Forces (London Dispersion Forces):
Dispersion forces are present in all molecules, regardless of polarity. These arise due to temporary fluctuations in electron density, which create temporary dipoles. In ethylene glycol, even though it has polar functional groups, the nonpolar carbon-hydrogen framework still contributes to dispersion forces. Therefore, dispersion forces are present in ethylene glycol.
2. Dipole-Dipole Interactions:
Ethylene glycol is a polar molecule. Each hydroxyl group (–OH) contains a polar O–H bond, and the molecule itself has an overall net dipole. Because of the permanent dipole moments due to electronegativity differences (oxygen is more electronegative than hydrogen or carbon), dipole-dipole interactions occur between neighboring ethylene glycol molecules. These interactions are stronger than dispersion forces but weaker than hydrogen bonds.
3. Hydrogen Bonding:
Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is directly bonded to a highly electronegative atom such as oxygen (O), nitrogen (N), or fluorine (F). In ethylene glycol, the O–H groups allow both donation and acceptance of hydrogen bonds. Each –OH group can:
- Act as a hydrogen bond donor (through the H)
- Act as a hydrogen bond acceptor (through the lone pairs on O)
Thus, ethylene glycol molecules can form extensive hydrogen bonding networks, making this the strongest IMF present in the substance.
Summary:
Because of its molecular structure, ethylene glycol exhibits:
- Dispersion forces (present in all molecules),
- Dipole-dipole interactions (due to its polarity),
- Hydrogen bonding (due to its –OH groups).
Hence, the correct choice is:
Dispersion, dipole-dipole, and H-bonding.