Q15 / 180 · KCET 2017 · Chemistry
In which of the following, homolytic bond fission takes place ?
- AAlkaline hydrolysis of ethyl chloride
- BAddition of \( \mathrm{HBr} \) to double bond
- Correct answerCFree radical chlorination of methane
- DNitration of Benzene
Solution
Homolytic bond fission takes place in free radical chlorination of methane.
\[ \mathrm{CH}_{3}-\mathrm{H}+\mathrm{Cl}_{2} \stackrel{520-670 \mathrm{~K}}{\text { or hv }}>\mathrm{CH}_{3}-\mathrm{Cl}+\mathrm{HCl} \]
The reaction occurs by a free radical mechanism which involves the following \( 3 \) steps:
Step 1: Chain initiation
Step 2: Chain propagation
\[ \begin{array}{l} \mathrm{CH}_{4}+\underset{\text { Methane }}{\mathrm{Cl}}+\underset{\text { Chlorine free radical }}{\mathrm{Cl}} \mathbf{~} \mathbf{~ H}_{3}+\mathrm{H} \mathrm{Cl} \\ \mathrm{CH}_{3}+\mathrm{Cl}-\mathrm{Cl} \stackrel{\mathrm{hv}}{\rightarrow} \mathrm{CH}_{3}-\mathrm{Cl}+\mathrm{Cl} \\ \mathrm{CH}_{3} \mathrm{Cl}+\mathrm{Cl} \rightarrow \mathrm{CH}_{2} \mathrm{Cl}+\mathrm{HCl} \\ \mathrm{CH}_{2} \mathrm{Cl}+\mathrm{Cl}-\mathrm{Cl} \rightarrow \mathrm{CH}_{2} \mathrm{Cl}_{2}+\mathrm{Cl} \end{array} \]
Step 3: Chain termination
\[ \begin{array}{l} \mathrm{Cl}+\mathrm{Cl} \rightarrow \mathrm{Cl}-\mathrm{Cl} \\ \mathrm{CH}_{3}+\mathrm{CH}_{3} \rightarrow \mathrm{CH}_{3}-\mathrm{CH}_{3} \\ \text { (Ethane) } \\ \mathrm{CH}_{3}+\mathrm{Cl} \rightarrow \mathrm{CH}_{3}-\mathrm{Cl} \end{array} \]
\[ \mathrm{CH}_{3}-\mathrm{H}+\mathrm{Cl}_{2} \stackrel{520-670 \mathrm{~K}}{\text { or hv }}>\mathrm{CH}_{3}-\mathrm{Cl}+\mathrm{HCl} \]
The reaction occurs by a free radical mechanism which involves the following \( 3 \) steps:
Step 1: Chain initiation
Step 2: Chain propagation
\[ \begin{array}{l} \mathrm{CH}_{4}+\underset{\text { Methane }}{\mathrm{Cl}}+\underset{\text { Chlorine free radical }}{\mathrm{Cl}} \mathbf{~} \mathbf{~ H}_{3}+\mathrm{H} \mathrm{Cl} \\ \mathrm{CH}_{3}+\mathrm{Cl}-\mathrm{Cl} \stackrel{\mathrm{hv}}{\rightarrow} \mathrm{CH}_{3}-\mathrm{Cl}+\mathrm{Cl} \\ \mathrm{CH}_{3} \mathrm{Cl}+\mathrm{Cl} \rightarrow \mathrm{CH}_{2} \mathrm{Cl}+\mathrm{HCl} \\ \mathrm{CH}_{2} \mathrm{Cl}+\mathrm{Cl}-\mathrm{Cl} \rightarrow \mathrm{CH}_{2} \mathrm{Cl}_{2}+\mathrm{Cl} \end{array} \]
Step 3: Chain termination
\[ \begin{array}{l} \mathrm{Cl}+\mathrm{Cl} \rightarrow \mathrm{Cl}-\mathrm{Cl} \\ \mathrm{CH}_{3}+\mathrm{CH}_{3} \rightarrow \mathrm{CH}_{3}-\mathrm{CH}_{3} \\ \text { (Ethane) } \\ \mathrm{CH}_{3}+\mathrm{Cl} \rightarrow \mathrm{CH}_{3}-\mathrm{Cl} \end{array} \]
Hence, the correct answer is option: 'C'.