Question

Correct order for the rate of dehydration of the given compounds with $H_{2}S{O}_4$ is:

• A. $I>II>III>IV$
• B. $IV>II>I>III$
• C. $I>II>IV>III$
• D. $III>IV>II>I$

Answer 1

The correct option is C $I>II>IV>III$

Rate of dehydration is governed by the stability of carbocation formed in the intermediate step. More the stability of the carbocation, more will be the rate.
In the given molecules, $\left(I\right)$ has the highest number of hyperconjugating structure and $\left(III\right)$ has the least. Therefore $\left(I\right)$ will form the most stable carbocation and $\left(III\right)$ will form the least stable carbocation.
Hence, the order of reaction is $I>II>IV>III$.