Why do branched alkanes have a lower boiling point than linear alkanes with the same molecular formula?

• A. Branched alkanes have weaker hydrogen bonding interactions than linear alkanes.
• B. They don't. Branched alkanes have higher boiling points than linear alkanes with the same molecular formula.
• C. Branched alkanes have a smaller surface area relative to linear alkanes, which leads to weaker dispersion forces.
• D. Branched alkanes have weaker dipoles, which leads to fewer dipole-dipole interactions.

Answer: (C)

Verified step by step guidance

1. Understand the concept of boiling point: The boiling point of a substance is the temperature at which its vapor pressure equals the external pressure. It is influenced by the strength of intermolecular forces present in the substance.
2. Identify the types of intermolecular forces in alkanes: Alkanes are nonpolar molecules, so the primary intermolecular forces are London dispersion forces, which are weak and arise from temporary dipoles.
3. Compare the surface area of branched vs. linear alkanes: Linear alkanes have a larger surface area compared to their branched counterparts. A larger surface area allows for more contact between molecules, leading to stronger dispersion forces.
4. Relate surface area to boiling point: Since linear alkanes have stronger dispersion forces due to their larger surface area, they require more energy (higher temperature) to overcome these forces, resulting in a higher boiling point.
5. Conclude why branched alkanes have lower boiling points: Branched alkanes have a smaller surface area, leading to weaker dispersion forces and thus a lower boiling point compared to linear alkanes with the same molecular formula.