Question

Which of the following alcohol is dehydrated most easily by concentrated $\ce{H_2SO_4}$

• A. $\ce{p - O2NC6 H4 CH (OH) CH3}$
• B. $\ce{p - ClC6 H4 CH (OH) CH3}$
• C. $\ce{p - CH3 OC6 H4 CH (OH) CH3}$
• D. $\ce{C6 H5 CH (OH) CH3}$

Answer 1

Answer: (C)

The case of dehydration of alcohol takes place most easily in case $(c)$.
In all cases during dehydration carbocation is formed.
In case $(a)$, carbocation destabilise by $NO_2(− I)$ group hence, dehydration reaction proceed with difficulty.
In case $(b)$ dehydration reaction takes place less difficulty than case $(a)$ because $Cl$ group show $(−I)$ and $(+R)$ effect.
In case $(c)$ dehydration reaction proceed easily because carbocation is stabilised by $OCH_3(+R)$ group.