Dec 12, 2016

When a halogen is substituted onto a molecule via free radical substituion.

#### Explanation:

An example of this reaction is the halogenation of methane.

$\text{CH"_4 + "C"l_2 (+"UV light")rarr "CH"_3"C"l + "HC} l$

In this reaction, methane reacts with the free radical $\text{C} l \cdot$. This radical is formed when the bond chlorine in a chlorine molecule is broken so that each atom gets one electron - this is known as homolytic fission.

$\text{C"l_2(+"UV light")rarr"C"l*+"C} l \cdot$

These radicals then react with methane in a free radical halogenation reaction to form chloromethane.