Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Types of peroxides, from top to bottom: peroxide ion, organic peroxide, organic hydroperoxide, peracid. The peroxide group is marked in blue. R, R1 and R2 mark hydrocarbon moieties.
Peroxides are a group of compounds with the structure R−O−O−R, where R = any element. The O−O group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable.
The most common peroxide is hydrogen peroxide (H2O2), colloquially known simply as "peroxide". It is marketed as solutions in water at various concentrations. Many organic peroxides are known as well.
Structure and dimensions of H2O2.
In addition to hydrogen peroxide, some other major classes of peroxides are: