Peroxynitrous acid (HNO₃) is a

reactive nitrogen species Reactive nitrogen species (RNS) are a family of antimicrobial molecules derived from nitric oxide (•NO) and superoxide (O2•−) produced via the enzymatic activity of inducible nitric oxide synthase 2 (Nitric oxide synthase 2A, NOS2) and NADPH ...

(RNS). It is the

conjugate acid A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid gives a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as it loses a hydrogen ion in the rever ...

of peroxynitrite (ONOO⁻). It has a p''K''_a of approximately 6.8. It is formed ''in vivo'' from the diffusion-controlled reaction of nitrogen monoxide (ON^•) and

superoxide In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula . The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of t ...

(). It is an isomer of

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

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. Peroxynitrous acid is also important in

atmospheric chemistry Atmospheric chemistry is a branch of atmospheric science that studies the chemistry of the Earth's atmosphere and that of other planets. This multidisciplinary approach of research draws on environmental chemistry, physics, meteorology, comput ...

References

{{Nitrogen compounds Nitrogen oxoacids Peroxy acids Nitrogen(III) compounds