Question

Which of the following statements regarding electrophilic aromatic substitution is wrong?
(A) Acetyl and cyano substituents are both deactivating and m-directing
(B) Alkyl groups are activating and o,p-directing
(C) Ammonio groups are m-directing but amino groups are o,p-directing
(D) Chloro and methoxy substituents are both deactivating and o,p-directing.

Answer 1

Hint: As we know that an electrophilic aromatic substitution reaction is the one in which an atom which is attached to an aromatic system that is generally a hydrogen has been replaced by the electrophile and some of the examples are aromatic nitration, Friedel-Crafts alkylation as well as acylation, aromatic sulfonation and halogenation.

Complete Step by step answer:
- We are well aware that an electrophilic aromatic substitution reaction is the one in which an atom attached to the aromatic ring that is generally a hydrogen has been replaced by an electrophile and some of the examples of such reactions includes: Aromatic nitration, Friedel-Crafts alkylation as well as acylation, aromatic sulfonation and halogenation.
- We should know that ortho-directing are the groups which substitute the hydrogen attached at ortho position or second carbon of the aromatic ring, p-directing are the one that substitute hydrogen at para position or third carbon of aromatic ring and the p-directing are those that substitute hydrogen at para or fourth position in aromatic ring.
- Also remember that activating groups are those that increase the rate of electrophilic aromatic substitution and deactivating groups are those that decrease the rate.
- Let us now discuss the given options on the basis of the above explanation. We know that Acetyl and Cyano groups are electron withdrawing groups and add the substituents to the meta- position thereby deactivating the ring.
- We also know that Alkyl groups are electron donating and cause the addition of electrophile on ortho and para positions. Ammonia groups are electron deficient and electron withdrawing hence meta-directing and amino groups are highly activating groups so ortho and para-directing.
- Chloro substituents are deactivating as they are very much electronegative, hence electron withdrawing in nature thus ortho, para-directing but methoxy is an activating group thus it is incorrect.

Hence the correct answer is (D).

Note: Remember substituents like hydroxyl groups, ethers, amines, alkyl groups, halogen and thiols are ortho and para-directing in nature and substituents like nitriles, carbonyls compounds, sulphones, electron deficient alkyl groups, nitro groups and alkylammonium are meta-directing in nature.