Question

Rank the following compounds in order of decreasing reactivity toward electrophilic substitution (most reactive first).
$\left(I\right)$ Chlorobenzene
$\left(II\right)$ 4-nitrochlorobenzene
$\left(III\right)$ 2,4-dinitrochlorobenzene
$\left(IV\right)$ 2,4,6-trinitrochlorobenzene

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

Answer 1

Answer: (A)

$I>II>III>IV$

$C{l}^{-}$ is a weakly deactivating group but due to its $+M$ effect it is ortho, para directing.

$N{O}_2^{-}$ is a strongly deactivating group and as no of a group, increases ring become less electron dense.

So an order of reactivity is-$I>II>III>IV$

Hence option A is correct.