Alkenes Structure and Reactivity

Ethylene and propylene are the two most important organic chemicals produced industrially. 

Ethylene, propylene and butene are synthesized by thermal cracking. 

The degree of unsaturation of a molecule describes the number of multiple bonds and/or rings a molecule has. 

To calculate degree of unsaturation of a compound, first determine the equivalent hydrocarbon formula of the compound. 

Calculate the number of pairs of hydrogens that would be present in an alkane C H2 + 2 that has the same number of carbons as the equivalent hydrocarbon of the compound of interest. The difference is the degree of unsaturation. 

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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 cv-pinene is the major component of turpentine. Life itself would be impossible without such alkenes as -carotene, a compound that contains 11 double bonds. An orange pigment responsible for the color of carrots, /3-carotene is a valuable dietary soiirce of vitamin A and is thought to offer some protection against certain types of cancer. 

Carbon-carbon double bonds are present in most organic and biological molecules, so a good understanding of their behavior is needed. In this chapter, we ll look at some consequences of alkene stereoisomerism and then focus on the broadest and most general class of alkene reactions, the electrophilic addition reaction. 

Ethylene, propylene, and butene are synthesized industrially by thermal cracking of light (C2-C8) alkanes. 

Compounds derived industrially from ethylene [WWi propylene. 

Ethylene oxide Ethylene glycol Ethylene dichloride Vinyl chloride 

Because of its double bond, an alkene has fewer hydrogens than an alkane with the same number of carbons—C H2 for an alkene versus C H2 . 2 for an alkane—and is therefore referred to as unsaturated. Ethylene, for example, has the formula C2H4, whereas ethane has the formula C2H6. 

11 Evidence for the Mechanism of Electrophilic Additions Carbocation Rearrangements 

A Deeper Look— Bioprospecting Hunting for Natural Pr ucts 

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