Illustrated Glossary of Organic Chemistry

Per: (1) Refers to a molecule containing an oxygen-oxygen single bond.

Hydrogen peroxide
Peracetic acid
Isopropyl methyl peroxide

(2) Refers to a molecule in which all hydrogens bonded to carbon have been replaced by an atom of the same element such as fluorine or chlorine.

Shown here is perfluorooctanoic acid (PFOA), formerly used as a surfactant in numerous products. The use of this molecule is now under scrutiny because it is a toxicant and carcinogen in animals, and persists indefinitely in the environment, showing little or no biodegradation over time.