<Tr> <Td> </Td> <Td> </Td> </Tr> <P> Nitric oxide (nitrogen oxide, nitrogen monoxide) is a molecular, chemical compound with chemical formula of N O. One of several oxides of nitrogen, it is a colorless gas under standard conditions . Nitric oxide is a free radical--i.e., its bonding structure includes an unpaired electron, represented by the dot () on the nitrogen atom--and it is in the class of heteronuclear diatomic molecules that are of historic theoretical interest (for the insights they gave in formulating early modern theories of bonding). It is a particularly important intermediate in the chemical industry . In addition, nitric oxide is formed in nitrogen - oxygen mixtures at high - temperature conditions, such as those found in combustion systems including internal combustion piston engines, gas turbines, industrial furnaces, and boilers . It is also produced naturally by the extremely high air temperatures produced along the path of lightning in thunderstorms . </P> <P> In mammals including humans, nitric oxide is an important cellular signaling molecule involved in many physiological and pathological processes . It is a powerful vasodilator with a short half - life of a few seconds in the blood . Long - known pharmaceuticals such as nitroglycerine and amyl nitrite were found to be precursors to nitric oxide more than a century after their first use in medicine . Low levels of nitric oxide production are important in protecting organs such as the liver from ischemic damage . Nitric oxide production is associated with nonalcoholic fatty liver disease (NAFLD) and is essential for hepatic lipid metabolism under starvation . </P> <P> As a consequence of its importance in neuroscience, physiology, and immunology, nitric oxide was proclaimed "Molecule of the Year" in 1992 . Research into its function led to the 1998 Nobel Prize for discovering the role of nitric oxide as a cardiovascular signalling molecule . Nitric oxide should not be confused with nitrous oxide (N O), an anesthetic, or with nitrogen dioxide (NO), a brown toxic gas and a major air pollutant, the latter being a product to which nitric oxide is rapidly oxidized in air . </P>

Lewis structure for a nitric oxide no− ion