Organic Chemistry MCAT Practice Exam

Which intermolecular forces mainly determine boiling points of organic compounds?

1. London dispersion forces

2. Hydrogen bonding, dipole-dipole interactions, and Van der Waals forces

3. Ionic bonds

4. Coordination bonds

The correct answer is: Hydrogen bonding, dipole-dipole interactions, and Van der Waals forces

The boiling points of organic compounds are largely influenced by the types of intermolecular forces present in the molecules. Hydrogen bonding, along with dipole-dipole interactions and Van der Waals forces (which are synonymous with London dispersion forces in this context), plays a crucial role in determining how strong the attractions between molecules are. Hydrogen bonds are particularly significant in organic compounds containing O-H, N-H, or F-H bonds, where a highly electronegative atom creates a strong dipole that can interact with other similar dipoles, leading to higher boiling points. Dipole-dipole interactions contribute to the boiling point as they involve attractions between molecules with permanent dipoles due to differences in electronegativity. Van der Waals forces, which include London dispersion forces, are present in all molecules but are more pronounced in larger, more polarizable molecules. Although these forces are generally weaker compared to hydrogen and dipole-dipole interactions, they can still contribute significantly to the overall boiling points, especially when evaluating heavier or more complex organic molecules. The other options don't primarily determine the boiling points in the context of organic compounds. Ionic bonds, for instance, are typically found in salts rather than organic compounds and can lead to high melting and boiling