Paraquat (trivial name; /ˈpærəkwɑːt/) or N,N′-dimethyl-4,4′-bipyridinium dichloride (systematic name) is the organic compound with the chemical formula [(C₆H₇N)₂]Cl₂. It is classified as a viologen, a family of redox-active heterocycles of similar structure. This salt is one of the most widely used herbicides. It is quick-acting and non-selective, killing green plant tissue on contact. It is also toxic to human beings and animals. It is linked to development of Parkinson's disease. The name is derived from the para positions of the quat ernary nitrogens. Quantities are sometimes expressed by cation mass alone (paraquat cation, paraquat ion); other salts (with other anions besides chloride) exist. In fact, its redox activity, which produces superoxide anions, is why it is toxic.