CHLORINATION OF AN ALKANE-A RADICAL REACTION

Now let s consider a reaction in which bonds break homolytically to give radicals that combine to form a new molecule. When radicals combine, the process is called homogenic bond formation. Methane reacts with chlorine gas at elevated temperatures or in the presence of ultraviolet light as an energy source. In this reaction, a chlorine atom replaces a hydrogen atom. 

The mechanism of this reaction requires several steps. 

Step 1. Initiation. A chlorine molecule absorbs energy, from either ultraviolet hght or high temperatures, and the Cl—Cl bond breaks homolytically to give two chlorine atoms. They are electron-deficient, highly reactive radicals. This step statts the reaction and is called the initiation step. 

Step 2. Propagation. A chlorine atom abstracts a hydrogen atom from methane, breaking a C—H bond and making an H—Cl bond. This step, which continues the reaction by generating a new radical, is called a propagation step. 

Step 3. Propagation. A Cl—Cl bond breaks and a C—Cl bond forms. A radical reacts and another radical forms. This is also a propagation step. 

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