.1.2.3 Olefin or Ethylene Series (Alkenes) Formula: CnH2n
Olefins are the second type of hydrocarbon important to us. Olefins are not found naturally in crude oil, but are the product of the refining process.

The olefin group of compounds is a simple straight chain series in which all the names end in -ene. Ethylene (ethene) C2H4 is the simplest molecule in the series.Hydrocarbons in this series combine easily with other atoms like chlorine and bromine, without the replacement of a hydrogen atom. Since they are so reactive, they are called unsaturated hydrocarbons.Unlike the paraffins, the maximum bonding capacity of the carbon atom is not fully satisfied by hydrogen or carbon atoms. Two adjacent carbon atoms form a "temporary" bond (in the absence of other available atoms) to meet bonding requirements fixed by valence. It is a necessary but unstable alliance. The structural formula for the olefins uses a double line to indicate the double carbon-carbon linkage, the most reactive point in the molecule.

What distinguishes olefins from Paraffins is that olefins are unsaturated. C2 paraffin, ethane, was saturated because it contained six hydrogen atoms. If we remove two of the hydrogen’s and bend the two vacated carbon valence bonds around to join with each other, we create a double bond or unsaturated bond. The resulting compound is ethylene, the C2 olefin.