Question

In the following reactions, if the rate of reaction of (I) and (II) are different, then, both reactions proceed by which mechanism?

• A. $E1$
• B. $E2$
• C. None of the above
• D. Anti-elimination

Answer 1

The correct option is B $E2$

The given reactions are elimination reaction. In reaction (II), there is a abstraction of $D$ while in reaction (I) there is a abstraction of H. Since, $D$ shows isotopic effect the rate of abstraction of D will differ with rate abstraction of H of same base.
Hence, both the reaction are of different rate because mechanism depends on the abstraction of H/D by the base.
In E1 elimination mechanism, the rate of reaction depends only the carbocation formation step so it does not have the isotopic effect.