Answer:
1,1,1-trichloroethane being a saturated halogenated alkane will undergo substitution reaction via free radical mechanism. The mechanism is divided in three steps,
Step 1: Initiation:
In this step the reaction is started by treating the chlorine gas either with UV light or by sunlight. This results in the formation of free radical.
Step 2: Propagation:
In this step the radical formed will react with the hydrogen atom resulting in formation of HCl and generating free radical of corresponding alkane. Hence, the radical will agian react with Cl2 molecule generating another Chlorine radical and corresponding halogenated compound i.e. 1,1,1,2-tetrachloroethane.
Step 3: Termination:
This is the last step. In this step the reaction is stopped/terminated. The free radicals react with each other forming a single bonds and stopping the formation of further radicals.
The mechanism is shown below,
