Question

Choose the false statement.
(A)- $-N{{H}_{2}}$ is strongly activating while $-NHCOC{{H}_{3}}$is activating.
(B)- $-N{{O}_{2}}$ is strongly deactivating while $-CHO$ is deactivating.
(C)- $-NHCOR$ and $-CH=O$ are m-directing.
(D)- $-C{{F}_{3}}$ and $-CR=O$ are m-directing.

Answer 1

If the functional group is electron-donating such that it increases the electron-density on the benzene ring and makes it susceptible for attack. Whereas an electron-withdrawing group will deactivate the ring.

Complete answer:
From the given statements, in order to determine the activating or deactivating nature of the functional group attached to the benzene ring as substituent, the presence of resonance effect and the inductive effect by the group is seen.
As through the resonance effect or the inductive effect, the tendency of the group to donate or withdraw the electrons away from the benzene ring will tell us about the electron-density over the benzene at the ortho-, meta- and para- position, making it susceptible for reaction.
So, in $-N{{H}_{2}}$due to the presence of the lone pair of electrons over the nitrogen atom, it can share its electron with the benzene ring through a positive resonance effect. Thus, increasing the electron-density over the ortho- and para -position and activating the ring for reaction.
Whereas, due to the carbonyl group attached to the nitrogen atom in $-NHCOC{{H}_{3}}$. It is under cross conjugation with the carbonyl group and the benzene ring. Thus, is weakly activating in nature and it is also ortho- and para- activator in the resonance.
Similarly, the nitro group, the $-CHO$, the $-C{{F}_{3}}$ and the $-CR=O$ being electron-withdrawing in nature, decrease the electron-density in the ring at the ortho- and the para-position. Thus, acting as deactivators and are meta-directing in nature.

Therefore, the false statement is option (C)- $-NHCOR$ and $-CH=O$ are m-directing. As $-NHCOR$ is a weakly activator at the ortho- and the para- position in the benzene ring.

Note:
The activators are generally ortho- and para- directing in nature, whereas the deactivators are meta-directing in nature as they reduce the electron-density at ortho- and para- position.