
Nitric oxide
Colorless gas with the formula NO / From Wikipedia, the free encyclopedia
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Nitric oxide (nitrogen oxide or nitrogen monoxide[1]) is a colorless gas with the formula NO. It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its chemical formula (•N=O or •NO). Nitric oxide is also a heteronuclear diatomic molecule, a class of molecules whose study spawned early modern theories of chemical bonding[6].
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Names | |||
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IUPAC name
Nitrogen monoxide[1] | |||
Systematic IUPAC name
Oxidonitrogen(•)[2] (additive) | |||
Other names
Nitrogen oxide Nitrogen(II) oxide Oxonitrogen Nitrogen monoxide | |||
Identifiers | |||
3D model (JSmol) |
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3DMet | |||
ChEBI | |||
ChEMBL | |||
ChemSpider |
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DrugBank |
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ECHA InfoCard | 100.030.233 ![]() | ||
EC Number |
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451 | |||
KEGG |
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PubChem CID |
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RTECS number |
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UNII | |||
UN number | 1660 | ||
CompTox Dashboard (EPA) |
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Properties | |||
NO | |||
Molar mass | 30.006 g·mol−1 | ||
Appearance | Colourless gas | ||
Density | 1.3402 g/L | ||
Melting point | −164 °C (−263 °F; 109 K) | ||
Boiling point | −152 °C (−242 °F; 121 K) | ||
0.0098 g / 100 ml (0 °C) 0.0056 g / 100 ml (20 °C) | |||
Refractive index (nD) |
1.0002697 | ||
Structure | |||
linear (point group C∞v) | |||
Thermochemistry | |||
Std molar entropy (S⦵298) |
210.76 J/(K·mol) | ||
Std enthalpy of formation (ΔfH⦵298) |
90.29 kJ/mol | ||
Pharmacology | |||
R07AX01 (WHO) | |||
License data | |||
Inhalation | |||
Pharmacokinetics: | |||
good | |||
via pulmonary capillary bed | |||
2–6 seconds | |||
Hazards | |||
Occupational safety and health (OHS/OSH): | |||
Main hazards |
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GHS labelling: | |||
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Danger | |||
H270, H280, H314, H330[4][3] | |||
P220, P244, P260, P280, P303+P361+P353+P315, P304+P340+P315, P305+P351+P338+P315, P370+P376, P403, P405[4][3] | |||
NFPA 704 (fire diamond) | |||
Lethal dose or concentration (LD, LC): | |||
LC50 (median concentration) |
315 ppm (rabbit, 15 min) 854 ppm (rat, 4 h) 2500 ppm (mouse, 12 min)[5] | ||
LCLo (lowest published) |
320 ppm (mouse)[5] | ||
Safety data sheet (SDS) | External SDS | ||
Related compounds | |||
Related nitrogen oxides |
Dinitrogen pentoxide Dinitrogen tetroxide | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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An important intermediate in industrial chemistry, nitric oxide forms in combustion systems and can be generated by lightning in thunderstorms. In mammals, including humans, nitric oxide is a signaling molecule in many physiological and pathological processes.[7] It was proclaimed the "Molecule of the Year" in 1992.[8] The 1998 Nobel Prize in Physiology or Medicine was awarded for discovering nitric oxide's role as a cardiovascular signalling molecule.[9]
Nitric oxide should not be confused with nitrogen dioxide (NO2), a brown gas and major air pollutant, or with nitrous oxide (N2O), an anesthetic gas.[6]