Question

Chlorination of alkanes is an example of ----- reaction.
A. Radical
B. Free radical
C. Elimination
D. None of these

Answer 1

Hint: Chlorination of alkanes means addition of chlorine to alkanes. It is also called halogenation. Generally halogenation occurs in the presence of heat or sunlight. Halogenation is an example of substitution reaction.

Complete answer:
- Chlorination of alkanes takes place in presence of heat or sunlight.
- Before chlorine is going to react with alkane’s chlorine first undergoes hemolysis and forms chlorine free radicals.
- The formed chlorine free radicals react with alkanes and replace the hydrogen present in it.
- The chemical reaction of chlorination of methane is as follows.
$$\begin{array}{rl}& C{l}_2\stackrel{heatorhv}{\to }2C{l}^{\cdot }\\ & C{l}^{\cdot }+C{H}_4\to C{H}_3^{\cdot }+HCl\\ & C{H}_3^{\cdot }+C{l}^{\cdot }\to C{H}_{3}Cl+C{l}^{\cdot }\end{array}$$
- From the above chemical reaction we can see clearly that at the starting (initial step) hemolytic cleavage of chlorine generates chlorine free radicals in presence of sunlight.
- The formed chlorine free radical reacts with methane and forms methyl free radical and hydrogen chloride as the products.
- Later again the formed methyl free radical reacts with another chlorine free radical and forms chloromethane as the product.
- The total reaction follows through the mechanism of free radical substitution reaction.
- Therefore chlorination of alkanes is an example of free radical reaction.

- So, the correct option is B.

Note: Chlorination of alkanes is a general reaction in organic chemistry. In the chlorination reaction the hydrogen present in the alkanes is going to substitute by the chlorine free radicals and forms chloro alkane or alkyl halides as the product.