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Why can adding more fluorine atoms lower the boiling points of fluorocarbon compounds?

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organohalogen compound Vinyl chloride is an organohalogen compound that has important industrial applications. When treated with certain catalysts, vinyl chloride monomers undergo polymerization and form the larger compound known as polyvinyl chloride, or PVC. PVC is used in the manufacture of numerous products, including packaging films and water pipes.

Adding more fluorine atoms to organohalogen compounds can lower their boiling points because fluorine is the least polarizable of the halogens.1

Polarizability refers to how easily the electron cloud of an atom can be distorted by nearby electric fields. Higher polarizability typically leads to stronger London dispersion forces—the intermolecular attractive forces that hold molecules together—which in turn results in higher boiling points.1

Because fluorine has low polarizability, replacing other atoms with multiple fluorine atoms reduces the overall molecular polarizability of the compound. This weakening of the dispersion forces between molecules leads to lower boiling points in the liquid state. This effect is distinct from other halogens, where multiple substitution generally increases the boiling point due to their higher polarizability.1