Question

Which of the following cannot be considered as a mechanistic step in chain reaction of methane with ${Cl}_2$?

• A. ${Cl}_2⟶{Cl}^{\ast }$
• B. ${CH}_4+{Cl}^{\ast }⟶{CH}_{3}Cl+H^{\ast }$
• C. ${Cl}^{\ast }+{CH}_4⟶{CH}_3+HCl$
• D. ${Cl}^{\ast }+{CH}_3⟶{CH}_{3}Cl$

Answer 1

The correct option is B ${CH}_4+{Cl}^{\ast }⟶{CH}_{3}Cl+H^{\ast }$

The mechanism of chlorination of methane involves the following steps

First is the chain initiation step : $C{l}_2+hv\to 2C{l}^{\bullet }$

Second is the chain propagation step : $C{H}_4+C{l}^{\bullet }\to C{H}_3+HCl$

Third is the chain termination step:$C{l}^{\bullet }+C{H_3}^{\bullet }\to C{H}_{3}Cl$

So the step not involved here is $C{H}_4+C{l}^{\bullet }\to C{H}_{3}Cl+C{l}^{\bullet }$

Hence the correct answer is option B