Nitric oxide

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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Nitric oxide

Names
IUPAC name Nitrogen monoxide[1]
Systematic IUPAC name Oxidonitrogen(•)[2] (additive)
Other names Nitrogen oxide Nitrogen(II) oxide Oxonitrogen Nitrogen monoxide
Identifiers
CAS Number	10102-43-9 Y
3D model (JSmol)	Interactive image
3DMet	B00122
ChEBI	CHEBI:16480 Y
ChEMBL	ChEMBL1200689 N
ChemSpider	127983 Y
DrugBank	DB00435 Y
ECHA InfoCard	100.030.233
EC Number	233-271-0
Gmelin Reference	451
IUPHAR/BPS	2509
KEGG	D00074 Y
PubChem CID	145068
RTECS number	QX0525000
UNII	31C4KY9ESH Y
UN number	1660
CompTox Dashboard (EPA)	DTXSID1020938
InChI InChI=1S/NO/c1-2 Y Key: MWUXSHHQAYIFBG-UHFFFAOYSA-N Y InChI=1/NO/c1-2 Key: MWUXSHHQAYIFBG-UHFFFAOYAI
SMILES [N]=O
Properties
Chemical formula	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)
Solubility in water	0.0098 g / 100 ml (0 °C) 0.0056 g / 100 ml (20 °C)
Refractive index (nD)	1.0002697
Structure
Molecular shape	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
ATC code	R07AX01 (WHO)
License data	EU EMA: by INN
Routes of administration	Inhalation
Pharmacokinetics:
Bioavailability	good
Metabolism	via pulmonary capillary bed
Biological half-life	2–6 seconds
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Fatal if inhaled Causes severe burns Causes eye damage Corrosive to the respiratory tract [3]
GHS labelling:
Pictograms	[4][3]
Signal word	Danger
Hazard statements	H270, H280, H314, H330[4][3]
Precautionary statements	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)	3 0 3 OX
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 Dinitrogen trioxide Nitrogen dioxide Nitrous oxide Nitroxyl (reduced form) Hydroxylamine (hydrogenated form)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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]