Any salt or ester of nitrous acid (HNO 2 ).
The salts are inorganic compounds with ion (NO 2 - ) and any cation . The esters are organic compounds with covalent bonds , having the structure R―O―N―O, in which R represents a carbon-containing combining group and the bonding is from carbon to oxygen. These covalent nitrites are constitutional isomers (see isomerism ) of the nitro compounds , nitric acid derivatives (R―NO 2 ), in which the bonding is from carbon to nitrogen. Nitrites are used as food preservatives and color enhancers, though they are so toxic they have caused deaths and combine with {{link=amine">amines to produce carcinogens . They are used in medicine to dilate blood vessels.