The key difference between "per" and "poly" as prefixes in chemistry, particularly when discussing fluorinated substances, lies in the extent of fluorination.
| Feature | Per- | Poly- |
|---|---|---|
| Fluorination | Complete | Incomplete |
| Carbon Chain | All C atoms fluorinated | At least one C atom not fully fluorinated |
| Example | Perfluorooctanoic acid (PFOA) | Polyfluoroalkyl substances |
Detailed Explanation
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Per-: When a chemical compound is described as "perfluorinated", it means that all the hydrogen atoms attached to the carbon chain have been replaced by fluorine atoms. The carbon chain is completely fluorinated.
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Poly-: In contrast, "polyfluorinated" indicates that some, but not all, of the hydrogen atoms on the carbon chain have been replaced by fluorine atoms. At least one carbon atom in the chain is not fully fluorinated. This means that the carbon atom has both fluorine and hydrogen atoms attached to it.
Example Breakdown
Consider per- and polyfluoroalkyl substances (PFAS) as highlighted in the provided reference:
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A perfluorinated chemical (like Perfluorooctanoic acid or PFOA) has all of its carbon-chain atoms fully fluorinated.
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A polyfluorinated chemical has at least one carbon atom in its chain that isn't fully fluorinated. This means it retains at least one carbon-hydrogen (C-H) bond.
