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{{Short description|Chemical compounds with the structure R–O–O–R'}}
{{Other uses}}
{{about|the molecule|the ion|inorganic peroxide}}
'''Peroxides''' are a group of [[molecules]] with the structure {{chem2|R\sO\sO\sR}}, where each R represents a radical (a portion of a complete molecule; not a [[free radical]]<ref>{{Cite web |title=Illustrated Glossary of Organic Chemistry |url=http://www.chem.ucla.edu/~harding/IGOC/R/r_group.html |access-date=June 19, 2024 |website=UCLA}}</ref>) and the O's are single [[oxygen]] atoms.<ref>{{Greenwood&Earnshaw2nd}}</ref>{{page missing|date=November 2025}}<ref>{{March6th}}</ref>{{page missing|date=November 2025}} Oxygen atoms are joined to each other and to adjacent elements through [[Single bond|single covalent bonds]], denoted by dashes or lines. The {{chem2|O\sO}} group in a peroxide is often called the '''peroxide group''', though some nomenclature discrepancies exist. This linkage is recognized as a common [[polyatomic ion]], and exists in many molecules.

== General structure ==
The characteristic structure of any regular peroxide is the oxygen–oxygen covalent single bond, which connects the two main atoms together. Each oxygen atom has a oxidation state of negative one, as 5 of its [[Valence electron|valence electrons]] remain in the outermost [[Atomic orbital|orbital shell]] whilst one is occupied in the [[covalent bond]]. Because of the nature of the covalent bond, this arrangement results in each atom having the equivalent of 7 valence electrons, [[Redox|reducing]] the oxygens and giving them a negative charge. This charge is affected by the addition of other elements, with the properties and structure changing depending on the added group(s).{{Citation needed|date=November 2025}}

== Common forms ==
[[File:Peroxide_group_v.2.png|left|thumb|324x324px|Types of peroxides, from top to bottom: [[peroxide ion]], [[organic peroxide]], [[hydroperoxide]], [[peracid]]. The peroxide group is marked in '''blue'''. R, R<sup>1</sup> and R<sup>2</sup> mark hydrocarbon [[Moiety (chemistry)|moieties]].]]
The most common peroxide is [[hydrogen peroxide]] ({{chem2|H2O2}}), colloquially known simply as "peroxide".<ref>{{Cite web |title=Hydrogen Peroxide {{!}} Hydrite.com |url=https://www.hydrite.com/Product/industrial/Hydrogen-Peroxide.htm |access-date=2025-11-12 |website=www.hydrite.com}}</ref> Many organic peroxides are known as well.

In addition to hydrogen peroxide, some other major classes of peroxides are:

* [[Peroxy acid|Peroxy acids]], the peroxy derivatives of many familiar acids, examples being [[peroxymonosulfuric acid]] and [[peracetic acid]], and their salts, one example of which is [[potassium peroxydisulfate]].
* [[Main group peroxides]], compounds with the linkage {{chem2|E\sO\sO\sE}} (E = [[main group element]]).{{multiple image
| direction         = vertical
| align             = right
| header            = 
| width             = 215
| image1            = H2O2 gas structure.svg
| alt1              = {{chem2|O\sO}} bond length = 147.4 pm <br />{{chem2|O\sH}} bond length = 95.0 pm
| caption1          = Structure and dimensions of {{chem2|H2O2}} in gas phase.
}}
* [[Metal peroxide|Metal peroxides]], examples being [[barium peroxide]] ({{chem2|BaO2}}), [[sodium peroxide]] ({{chem2|Na2O2}}) and [[zinc peroxide]] ({{chem2|ZnO2}}).
* [[Organic peroxide|Organic peroxides]], compounds with the linkage {{chem2|C\sO\sO\sC}} or {{chem2|C\sO\sO\sH}}. One example is [[Tert-Butyl hydroperoxide|''tert''-butylhydroperoxide]].

== Nomenclature ==
The linkage between the oxygen molecules is known as a '''peroxy group''' (sometimes called '''peroxo group,''' '''peroxyl group, of peroxy linkage'''). The nomenclature of the peroxy group is somewhat variable,<ref>{{GoldBookRef|title=peroxides|file=P04510}}</ref> and exists as an exception to the rules of naming polyatomic ions. This is because, when it was discovered, it was believed to be monatomic.<ref>{{Cite web |date=2004 |title=Nomenclature |url=https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch2/names.html |access-date=March 25, 2024 |website=Purdue Division of Chemical Education}}</ref>  The term was introduced by [[Thomas Thomson (chemist)|Thomas Thomson]] in 1804 for a compound combined with as much oxygen as possible,'''''<ref>{{Cite book |last=Thomson |first=Thomas |title=A System of Chemistry |date=1804 |publisher=Bell and Bradfute |edition=2nd |volume=1 |location=Edinburgh |publication-place=Edinburgh |publication-date=1804 |pages=division 1, page 103 |language=English |chapter=4 |via=Google books}}</ref>''''' or the oxide with the greatest quantity of oxygen.<ref>{{Cite web |last= Harper, Douglas. |title=Peroxide |url=https://www.etymonline.com/word/peroxide#:~:text=peroxide%20(n.),effective%20bleaching%20agent%20for%20hair). |website=Online Etymology Dictionary}}</ref> 

            
== References ==
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{{Functional groups}}
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[[Category:Peroxides| ]]