Physical properties
- Nitric oxide is a colorless gas with the formula NO.
- It is one of the principal oxides of nitrogen.
- Nitric oxide is a free radical with an unpaired electron.
- It is a heteronuclear diatomic molecule.
- Nitric oxide forms in combustion systems and can be generated by lightning in thunderstorms.
- The ground state electronic configuration of NO is (1σ)^2(2σ)^2(3σ)^2(4σ*)^2(5σ)^2(1π)^4(2π*)^1.
- The first two orbitals are pure atomic 1 and 1 from oxygen and nitrogen respectively.
- Orbitals noted with an asterisk are antibonding.
- The lone electron in the 2π orbital makes NO a doublet (X ²Π) in its ground state.
- The degeneracy of the doublet is split in the fine structure.
- The dipole of NO is measured experimentally to be 0.15740 D.
- The dipole is oriented from O to N(⁻NO⁺) due to the transfer of negative electronic charge.
- Oxygen transfers electronic charge to nitrogen.

Reactions
- Upon condensing to a liquid, nitric oxide dimerizes to dinitrogen dioxide.
- The association between NO molecules is weak and reversible.
- NO can be decomposed to the elements.
- Nitric oxide converts into nitrogen dioxide when exposed to oxygen.
- This reaction is thought to occur via intermediates like ONOO and ONOONO.
- Nitric oxide reacts with transition metals to give complexes called metal nitrosyls.
- The most common bonding mode of nitric oxide is the terminal linear type (M−NO).
- Nitric oxide can also serve as a one-electron pseudohalide.
- The M−N−O group in nitric oxide complexes is characterised by an angle between 120° and 140°.
- Nitric oxide can bridge between metal centers through the nitrogen atom in various geometries.

Occupational safety and health
- The legal limit for nitric oxide exposure in the workplace is set at 25ppm (30mg/m³) over an 8-hour workday by OSHA.
- NIOSH recommends an exposure limit of 25ppm (30mg/m³) over an 8-hour workday.
- Nitric oxide is immediately dangerous to life and health at levels of 100ppm.
- Occupational exposure to nitric oxide can lead to respiratory issues and lung damage.
- Proper ventilation and personal protective equipment should be used to minimize exposure to nitric oxide in the workplace.

Explosion hazard
- Liquid nitrogen oxide is highly sensitive to detonation, even without fuel, and can be as explosive as nitroglycerin.
- Detonation of liquid nitric oxide near its boiling point (-152°C) can generate a 100 kbar pulse and cause equipment fragmentation.
- Nitric oxide is the simplest molecule capable of detonation in all three phases (gas, liquid, and solid).
- Industrial accidents have occurred due to the explosion of liquid nitric oxide during distillation.
- Gaseous nitric oxide has a detonation velocity of about 2300 m/s, while as a solid, it can reach a velocity of 6100 m/s.

Nobel Prize and research
- The Nobel Prize in Physiology or Medicine was awarded in 1998 for the discovery of the role of nitric oxide as a signaling molecule in the cardiovascular system.
- Research on nitric oxide donors and their development is an active area of study in pharmacology and medicine.
- Nitric oxide has been studied for its potential therapeutic applications, including its role in regulating blood pressure and as a vasodilator.
- Scientists have investigated the use of fluorescent indicators to detect and image nitric oxide in biological systems.
- The interaction between nitric oxide and other signaling molecules, such as hydrogen sulfide, is an area of ongoing research.

Nitric oxide (Wikipedia)

Not to be confused with nitrous oxide.

This article is about a molecule of one nitrogen atom and one oxygen atom. For other chemical combinations of nitrogen and oxygen, see nitrogen oxide. For the use of nitric oxide as a medication or in biology, see Biological functions of nitric oxide.

Nitric oxide (nitrogen oxide or nitrogen monoxide) 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.

Nitric oxide

Names
IUPAC name Nitrogen monoxide
Systematic IUPAC name Oxidonitrogen(•) (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
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H270, H280, H314, H330
Precautionary statements	P220, P244, P260, P280, P303+P361+P353+P315, P304+P340+P315, P305+P351+P338+P315, P370+P376, P403, P405
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)
LCLo (lowest published)	320 ppm (mouse)
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. It was proclaimed the "Molecule of the Year" in 1992. The 1998 Nobel Prize in Physiology or Medicine was awarded for discovering nitric oxide's role as a cardiovascular signalling molecule.

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.