Hydroxyl radical

This article is about the free radical OH.

• For the ion OH ^- see hydroxide ion .
• For the functional group -OH see hydroxyl group .
• For the group of substances see hydroxides .

The hydroxyl radical (OH radical, HO ·) is a molecule made up of one hydrogen and one oxygen atom. As a radical , it has a single, unpaired electron and is therefore very reactive. It is created in the troposphere from ozone and water molecules when UV rays strike and plays an important role in summer smog and in the breakdown of many trace gases . It is therefore called the detergent of the atmosphere .

Further formation reactions , some of which are also used in photoreactors to study air chemistry , are the photolysis of hydrogen peroxide

${\displaystyle \mathrm {HOOH\longrightarrow 2\ {\cdot }OH} }$

and nitrous acid

${\displaystyle \mathrm {HNO_{2}\longrightarrow {\cdot }OH+NO} }$

Hydroxyl radicals are also formed at night in the absence of solar radiation. The main source is considered to be the reaction of ozone with olefins , which proceeds via unstable alkenyl peroxides .

The OH radical also plays an important role in many combustion processes , e.g. B. in the oxyhydrogen reaction :

${\displaystyle \mathrm {H_{2}\ {\xrightarrow {Energie}}\ H{\cdot }+{\cdot }H\quad (Kettenstart)} }$

${\displaystyle \mathrm {H{\cdot }+O_{2}\longrightarrow {\cdot }OH+O{\cdot }} }$

${\displaystyle \mathrm {O{\cdot }+H_{2}\longrightarrow {\cdot }OH+H{\cdot }} }$

${\displaystyle \mathrm {{\cdot }OH+H_{2}\longrightarrow H_{2}O+H{\cdot }} }$

and other reactions

In 1963, OH was also measured in the interstellar medium using radio astronomical methods .

Web links

• Astromolecule of the month February 2009, astrochymist.org

Individual evidence

1. ↑ IPCC: Trends in the Hydroxyl Free Radical (IPCC AR4 WG1) (PDF): The hydroxyl free radical (OH) is the major oxidizing chemical in the atmosphere, destroying about 3.7 Gt of trace gases, including CH4 and all HFCs and HCFCs, each year (Ehhalt, 1999).
2. ^ R. Atkinson, J. Arey, Atmospheric Environment 2003, 37, Supplement 2, 197-219. doi : 10.1016 / S1352-2310 (03) 00391-1
3. ^ S. Weinreb, et al .: Radio Observations of OH in the Interstellar Medium. in: Nature 200, pp. 829-831 (November 30, 1963); doi : 10.1038 / 200829a0
4. ↑ [e-mail], 1963 (Accessed on 1 July 2010)