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Peroxynitrous acid
Preferred IUPAC name
Peroxynitrous acid[citation needed]
Systematic IUPAC name
3D model (JSmol)
MeSH Peroxynitrous+Acid
  • InChI=1S/HNO3/c2-1-4-3/h3H checkY
  • OON=O
Molar mass 63.0128 g mol−1
Conjugate base Peroxynitrite
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Peroxynitrous acid (HNO3) is a reactive nitrogen species (RNS). It is the conjugate acid of peroxynitrite (ONOO). It has a pKa of approximately 6.8. It is formed in vivo from the diffusion-controlled reaction of nitrogen monoxide (ON) and superoxide (O•−
). 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.[3] Peroxynitrous acid is also important in atmospheric chemistry.


  1. ^ N.Connelly and T. Damhus, IUPAC. Nomenclature of Inorganic Chemistry, RSC Publishing, Cambridge, 2005
  2. ^ "Peroxynitrous Acid - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 11 April 2012.
  3. ^ Koppenol, W. H.; Bounds, P. L.; Nauser, T.; Kissner, R.; Rüegger, H. (2012). "Peroxynitrous acid: controversy and consensus surrounding an enigmatic oxidant". Dalton Transactions. 41: 13779–13787.