"An alkene, sometimes called an olefin, is a hydrocarbon that contains a carbon– carbon double bond. Alkenes occur abundantly in nature. … Ethylene and propylene, the simplest alkenes, are the two most important organic chemicals produced industrially. Approximately 127 million metric tons of ethylene and 54 million metric tons of propylene are produced worldwide each year for use in the synthesis of polyethylene, polypropylene, ethylene glycol, acetic acid, acetaldehyde, and a host of other substances."