Structure of the<unk>  group<unk> s (or more formally N-Nitrosamines) are organic compounds of the chemical structure R2N−N=O, where R is usually an alkyl group. They feature a nitroso group (NO+) bonded to a deprotonated amine. Most<unk> s are carcinogenic in nonhuman animals. A 2006 systematic review supports a "positive association between nitrite and<unk>  intake and gastric cancer, between meat and processed meat intake and gastric cancer and oesophageal cancer, and between preserved fish, vegetable and smoked food intake and gastric cancer, but is not conclusive".
Nitrosamine
Carbon monoxide
Nitrous oxide 
Nicosan
Benzene
Vinyl chloride
Nitrobenzene
N-Nitrosodimethylamine