Unsaturated compounds without added hydrogen

One major distinction separates the chemical properties of saturated hydrocarbons from those of the unsaturated hydrocarbons. By opening a multiple bond in an alkene or alkyne, the compound is capable of reacting by addition, simply by adding atoms of some element to the molecule. By contrast, an alkane molecule is literally saturated there is no more room for an atom to join the molecule without first removing a hydrogen atom. A reaction in which a hydrogen atom in an alkane is replaced by an atom of another element is called a substitution reaction. 

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