Question

Reaction of alkanes with halogens such as chlorine and bromine proceeds through.......

• A. Free radical substitution mechanism
• B. Electrophilic substitution mechanism
• C. Nucleophilic substitution mechanism
• D. Decomposition mechanism

Hint:

Think “halogen + light/heat” \(\Rightarrow\) radical chain: initiation, propagation, termination.

Answer 1

The Correct Option is A

Step 1: Identify hallmark mechanism.
Halogenation of alkanes (e.g., methane) under light/heat follows a free radical chain mechanism.
Step 2: Outline the steps (example with \( \mathrm{Cl_2} \)).
Initiation: \( \mathrm{Cl_2} \xrightarrow{h\nu/\Delta} 2\,\mathrm{Cl\cdot} \) (homolysis).
Propagation: \[ \begin{aligned} \mathrm{Cl\cdot + CH_4} &\rightarrow \mathrm{HCl + CH_3\cdot} \\ \mathrm{CH_3\cdot + Cl_2} &\rightarrow \mathrm{CH_3Cl + Cl\cdot} \end{aligned} \] Termination: Radical–radical coupling (e.g., \( \mathrm{Cl\cdot + Cl\cdot \rightarrow Cl_2} \)).
Step 3: Conclusion.
Thus, the process is free radical substitution.
Final Answer: \[ \boxed{\text{Free radical substitution mechanism}} \]