:Peroxynitrous acid

{{Refimprove|date=January 2007}}

{{Chembox

| PIN = Peroxynitrous acid{{Citation needed|date=April 2012}}

| SystematicName = (Hydridodioxido)oxidonitrogenN.Connelly and T. Damhus, IUPAC. Nomenclature of Inorganic Chemistry, RSC Publishing, Cambridge, 2005{{Cite web|title=Peroxynitrous Acid - Compound Summary|url=https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=123349&loc=ec_rcs|work=PubChem Compound|publisher=National Center for Biotechnology Information|accessdate=11 April 2012|location=USA|date=16 September 2004|at=Identification and Related Records}}

| ImageFile = Peroxynitrous-acid-2D.svg

| ImageSize = 250px

| ImageFile1 = cis-Peroxynitrous acid Ball and Stick.png

| ImageSize1 = 150

| ImageFile2 = trans-Peroxynitrous acid Ball and Stick.png

| ImageSize2 = 150

|Section1={{Chembox Identifiers

| CASNo = 14691-52-2

| CASNo_Ref = {{cascite|correct|??}}

| PubChem = 123349

| ChemSpiderID = 109951

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| MeSHName = Peroxynitrous+Acid

| ChEBI = 25942

| ChEBI_Ref = {{ebicite|correct|EBI}}

| ChEMBL = 1794794

| ChEMBL_Ref = {{ebicite|correct|EBI}}

| Gmelin = 49207

| SMILES = OON=O

| StdInChI = 1S/HNO3/c2-1-4-3/h3H

| StdInChI_Ref = {{stdinchicite|correct|chemspider}}

| StdInChIKey = CMFNMSMUKZHDEY-UHFFFAOYSA-N

| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

}}

|Section2={{Chembox Properties

| Formula = {{Chem|NHO|3}}

| MolarMass = 63.0128 g mol⁻¹

| ConjugateBase = Peroxynitrite

}}

|Section3={{Chembox Related

| OtherCompounds = {{Unbulleted list|Nitroxyl|Nitrous acid|Nitrosyl bromide|Nitrosyl chloride|Nitrosyl fluoride}}

}}

}}

Peroxynitrous acid (HNO₃) is a reactive nitrogen species (RNS). It is the conjugate acid of peroxynitrite (ONOO⁻). It has a pK_a of approximately 6.8. It is formed in vivo from the diffusion-controlled reaction of nitrogen monoxide (ON^•) and superoxide ({{chem|O|2|•−}}). It is an isomer of nitric acid and isomerises with a rate constant of k = 1.2 s⁻¹, a process whereby up to 5% of hydroxyl and nitrogen dioxide radicals may be formed. It oxidises and nitrates aromatic compounds in low yield. The mechanism may involve a complex between the aromatic compound and ONOOH, and a transition from the cis- to the trans-configuration of ONOOH.{{cite journal|first1=W. H. |last1=Koppenol |first2=P. L. |last2=Bounds |first3=T. |last3=Nauser |first4=R. |last4=Kissner |first5=H. |last5=Rüegger |title=Peroxynitrous acid: controversy and consensus surrounding an enigmatic oxidant |journal=Dalton Transactions |date=2012 |volume=41 |pages=13779–13787}} Peroxynitrous acid is also important in atmospheric chemistry.