Alkenes

Alkenes: The Olefins

Alkenes form a family of unsaturated hydrocarbons. The defining structural feature of every alkene is the presence of at least one carbon–carbon double bond ($\ce{C=C}$). Because a double bond uses two of the four bonding electrons of each carbon, the two carbon atoms involved are each bonded to fewer hydrogen atoms than they would be in an alkane.

General Formula and the Olefin Name

If an alkene contains exactly one double bond, each double bond reduces the hydrogen count by two relative to the corresponding alkane. An alkane with $n$ carbon atoms has the formula $\ce{C_nH_{2n+2}}$. Removing two hydrogens to form the double bond gives:

This is the general formula for alkenes with one double bond. The simplest member is ethene, $\ce{C2H4}$.

The older name for alkenes is olefins, meaning "oil-forming." This name comes from the reaction of ethene with chlorine, which produces an oily liquid (dichloroethane).