Question

Which of the following is not a possible termination step in the free radical ? chlorination of methane A. -CH3 + wall → CH3-wall B. CH3 + Cl. → CH3CI C. CH3 + CH3 – CH3CH3 D. CH3 + Cl2 → CH3Cl + CI E. CI + wall → Cl-wall

Answer 1

Answer : Among the above given steps the step shown as follows is not a possible termination step in the free radical chlorination of methane which is shown as follows :

(D) ^.CH₃ + Cl₂$\rightarrow$ CH₃Cl + Cl

This is due to the fact that, as we know, during chain termination step in the free radical chlorination of methane two free radical combine together to form neutral molecule such as two  ^.CH₃ free radical combine to form CH₃-CH₃ (as shown in C); two  ^.Cl free radical combine to form Cl₂ ; ^.CH₃ free radical combine with ^.Cl free radical to form CH₃Cl (as shown in B).

And step shown in (D) ^.CH₃ + Cl₂$\rightarrow$ CH₃Cl + Cl is chain propagation step in the free radical chlorination of methane instead of the chain termination step.

Thus, (D) ^.CH₃ + Cl₂$\rightarrow$ CH₃Cl + Cl is not a possible termination step in the free radical chlorination of methane.