Question

Select the chain propagation steps in the free radical chlorination of methane :-
(a) $Cl _{2} \longrightarrow 2 \dot{ C l}$
(b) $\dot{ C } l + CH _{4} \longrightarrow CH _{3} Cl + \dot{H}$
(c) $\dot{ C } l + CH _{4} \longrightarrow \dot{ CH }_{3}+ HCl$
(d) $\dot{ H }+ Cl _{2} \longrightarrow HCl +\dot{ C l}$
(e) $\dot{ C } H _{3}+ Cl _{2} \longrightarrow CH _{3}- Cl +\dot{ C } l$

• A. b, c, e
• B. a, c, e
• C. c, e
• D. b, c, d

Answer 1

Answer: (C)

(Free radical chlorination of methane)
$\Rightarrow $ FRSR
$CH _{4}+ Cl _{2} \xrightarrow{ hv} CH _{3}- Cl + HCl$
Mechanism :-
(i) Chain Initiation :-
$Cl _{2} \xrightarrow{ hv}2 \dot{ Cl }$
(ii) Chain Propagation

(iii) Chain Termination
$\dot{ CH }_{3}+\dot{ CH }_{3} \rightarrow CH _{3}- CH _{3}$
$\dot{ Cl} +\dot{ Cl } \rightarrow Cl - Cl $
$\dot{CH} _{3}+\dot{ Cl } \rightarrow CH _{3}- Cl $