The Carbon-Fluorine Bond: the Source of PFAS Stability

The exceptional stability of per- and polyfluoroalkyl substances (PFAS) is fundamentally rooted in the properties of the carbon-fluorine (C-F) bond. Fluorine is the most electronegative element, creating a highly polarized bond with carbon. This results in a short bond length (around 1.35 Å) and a very high bond dissociation energy, making it extremely difficult to break. In perfluoroalkyl substances, where all non-terminal carbons are fully saturated with fluorine atoms, this effect is amplified. The fluorine atoms create a helical sheath around the carbon backbone, sterically protecting it from chemical attack. This ‘fluorine shield’ also repels both water (hydrophobicity) and oils (oleophobicity), a rare combination that makes PFAS effective surfactants. The cumulative inductive effect of multiple fluorine atoms also strengthens adjacent C-C bonds within the chain, further contributing to the molecule’s overall inertness. This chemical robustness is why PFAS are dubbed “forever chemicals”; they do not readily break down under natural environmental conditions, leading to their widespread accumulation.