Question

Which of the following alcohol is dehydrated most easily by concentrated $\mathrm{H}{}_2\mathrm{SO}{}_4$

• A. $\mathrm{p}-\mathrm{O}{}_2\mathrm{NC}{}_6\mathrm{H}{}_4\mathrm{CH}(\mathrm{OH})\mathrm{CH}{}_3$
• B. $\mathrm{p}-\mathrm{ClC}{}_6\mathrm{H}{}_4\mathrm{CH}(\mathrm{OH})\mathrm{CH}{}_3$
• C. $\mathrm{p}-\mathrm{CH}{}_3\mathrm{OC}{}_6\mathrm{H}{}_4\mathrm{CH}(\mathrm{OH})\mathrm{CH}{}_3$
• D. $\mathrm{C}{}_6\mathrm{H}{}_5\mathrm{CH}(\mathrm{OH})\mathrm{CH}{}_3$

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 $N{O}_2(-I)$ 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 $OC{H}_3(+R)$ group.