Question

Which the following reaction will have the highest rate at a given temperature?

• A. $\text{1-chloro-4-nitrobenzene}\underset{\left(ii\right)H^{+}}{\overset{\left(i\right)O{H}^{-}}{\to }}\text{Product(s)}$
  
• B. $\text{1-chloro-2,4-dinitrobenzene}\underset{\left(ii\right)H^{+}}{\overset{\left(i\right)O{H}^{-}}{\to }}\text{Product(s)}$
  
• C. $\text{2-chloro-1,3,5-trinitrobenzene}\underset{\left(ii\right)H^{+}}{\overset{\left(i\right)O{H}^{-}}{\to }}\text{Product(s)}$
  
• D. All have equal rate of reaction.

Answer 1

The correct option is C $\text{2-chloro-1,3,5-trinitrobenzene}\underset{\left(ii\right)H^{+}}{\overset{\left(i\right)O{H}^{-}}{\to }}\text{Product(s)}$


More the number of EWG ( Electron withdrawing groups) attached to an aryl halide at ortho and para positions, more is the rate of reaction at a given temperature. This is because, the Meisenheimer complex formed after the attack of the nucleophile (here $O{H}^{-}$), is stabilized by $-M$ effect of the EWG group (here $-N{O}_2$).
In (a) there is only one group attached to the aryl halide at ortho position. In (b) there are two, whereas in (c) there are three $-N{O}_2$ groups attached which increases the stability of the intermediate the most.



Hence (c) has the highest rate of reaction