Question

Which of the following will not undergo nucleophilic aromatic substitution ?

• A. $I,II$ and $III$
• B. $II$ and $IV$
• C. $III$ and $IV$
• D. only $IV$

Answer 1

Answer: (D)

only $IV$

For nucleophilic aromatic substitution reactions to take place the presence of hydrogen at ortho-position is necessary. If $\beta$-hydrogen (hydrogen at ortho position) are absent then reaction will not take place.

In structure $IV$ at both the ortho position methyl group $\left(C{H}_3\right)$ is attached and hydrogen is absent. Therefore, it will not undergo nucleophilic substitution. While in structure $I,II$ and $III$, either hydrogen $\left(H\right)$ or deuterium $\left(D\right)$ is present at ortho position, hence, these will undergo nucleophilic substitution reaction.