Alkenes

Alkenes : Structure and reactivity
An alkene, sometimes called an olefin, is a hydrocarbon that contains a carbon– carbon double bond. Alkenes occur abundantly in nature. Ethylene, for instance, is a plant hormone that induces ripening in fruit, and a-pinene is the major component of turpentine. Life itself would be impossible without such alkenes as b-carotene, a compound that contains 11 double bonds. An orange pigment responsible for the color of carrots, b-caroteneThe C—C double bond is easily converted to other functional groups. Because of this, alkenes are important as intermediates in the synthesis of drugs, pesticides and other valuable chemicals. is an important dietary source of vitamin A and is thought to offer some protection against certain types of cancer.
The benefit of studying carbon–carbon double bonds are its present in most organic and biological molecules. This, however, accounts for only a small fraction of the billions of pounds of alkenes used annually to make polymers. Example: Polyethylene (PE):
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, as in the following Figure.