Question

The only o, p- directing group that is deactivating in nature is:
(A) $ \text{-N}{{\text{H}}_{\text{2}}} $
(B) $ \text{-OH} $
(C) $ \text{-X} $ (halogens)
(D) $ \text{-R} $ (alkyl groups)

Answer 1

Hint: When the aryl compounds undergo electrophilic substitution then they direct they direct the incoming electrophiles to three positions. Either they are directed to the ortho-para positions or they are directed to the meta positions. The group required is highly electronegative but acts as an electron donating group.

Complete step by step solution:
A functional group is an o, p- directing group when it directs the incoming electrophiles to the second, fourth, and sixth carbon atoms in the benzene ring as per the position of the group that directs them. The meta directing functional groups are those that direct the incoming electrophile to the third carbon atom with respect to the functional group that directs it.
There are different groups that behave as the o, p orienting groups and among them are the amino group, hydroxyl group, halogen groups, alkyl group, etc.
But the halogen groups are highly electronegative in nature but as they contain the lone pair of atoms in them that can go into extended conjugation with the electrons of the benzene therefore they act as the o, p-directing groups. But due to their highly electronegative nature they deactivate the benzene ring.
So the correct answer here is the $ \text{-X} $ (halogens) group, option C.

Note:
The groups that are meta directing are highly electron-withdrawing groups that include the nitro group $ \text{-N}{{\text{O}}_{\text{2}}} $ , the carboxyl group $ \text{-COOH} $ , the sulphurous acid group $ \text{-S}{{\text{O}}_{\text{3}}}\text{H} $ , the aryl group, and so on. The incoming electrophile is directed to the meta position because the above-mentioned groups draw the electrons mainly from the second, fourth, and the sixth positions by extended conjugation.