In organic chemistry, an alkene is an unsaturated hydrocarbon that contains at least one carbon–carbon double bond. Alkene, olefin, and olefine are used often interchangeably (see nomenclature section below). Acyclic alkenes, with only one double bond and no other functional groups, known as mono-enes, form a homologous series of hydrocarbons with the general formula CnH2n. Alkenes have two hydrogen atoms less than the corresponding alkane (with the same number of carbon atoms). The simplest alkene, ethylene (C2H4), which has the International Union of Pure and Applied Chemistry (IUPAC) name ethene is the organic compound produced on the largest scale industrially. Aromatic compounds are often drawn as cyclic alkenes, but their structure and properties are different and they are not considered to be alkenes.