Question

Which of the following is incorrect statement for the given reaction?

• A. Rate of formation of II and IV would be identical
• B. Rate of formation of I would be slower than that of III
  
• C. Formation of I would show primary isotope effect
  
• D. Formation of III involves E1 reaction
  

Answer 1

The correct option is D Formation of III involves E1 reaction

Option: $D$

As the sizes of the hydrogen and Deutrium are almost same, therefore the reaction rate is same in both hence, the rate of formation of II and IV is similar.

As Deuterium is heavier than hydrogen therefore it takes greater energy to break the $C-D$ bond as compared to $C-H$ bonds. As These are a part of Rate determining step therefore I is slower than III formation and formation of I also show primary Isotope effect.

It undergoes $E_2$ reaction as carbocation is not stable.

Mechanism:

$C{D}_3-\underset{\underset{Br}{|}}{CH}-C{D}_3\stackrel{KOH}{\underset{alc.}{\to }}C{D}_2=CH-C{D}_3+\underset{S{N}^{2}product}{C{D}_3-\underset{\underset{OH}{|}}{CH}-C{D}_3}$

$C{H}_3-\underset{\underset{Br}{|}}{CH}-C{H}_3\stackrel{KOH}{\underset{alc.}{\to }}C{H}_2=CH-C{H}_3+\underset{S{N}^{2}product}{C{H}_3-\underset{\underset{OH}{|}}{CH}-CH}$