Which of the following statement(s) is/are correct with reference to electrophilic substitution of \(C_6H_5Cl\)?

(A) \(Cl\) acts as an activating and \(o/p\) directing group.

(B) \(Cl\) acts as a deactivating and \(o/p\) directing group.

(C) acts as an activating and \(m-\) directing group.

(D) \(Cl\) acts as a deactivating and \(m-\)directing group.

(E) Presence of \(NO_2\) at \(p-\) position facilitates the reactions.

Choose the correct answer from the options given below:

B and E only

The correct answer is option 4. B and E only.

Let us break down each statement and understand the role of chlorine (\(Cl\)) and the nitro group (\(NO_2\)) in the context of electrophilic substitution reactions of chlorobenzene (\(C_6H_5Cl\)).

Electrophilic Substitution in Aromatic Compounds:

In aromatic compounds like chlorobenzene, electrophilic substitution reactions (e.g., nitration, sulfonation, halogenation) involve the substitution of a hydrogen atom on the benzene ring by an electrophile.

Chlorine (\(Cl\)) as a Substituent:

Chlorine is an interesting substituent because it has both inductive and resonance effects, which influence how it affects the reactivity of the benzene ring and the position where new groups are added.

Inductive Effect (-I effect)

Electronegativity: Chlorine is highly electronegative, meaning it pulls electron density away from the benzene ring through the sigma bond. This withdrawal of electron density makes the ring less reactive towards electrophiles (hence, **deactivating**).

Deactivation: The overall electron density of the ring decreases, making the ring less attractive to electrophiles.

Resonance Effect (+R effect):

Lone Pair Donation: Chlorine has lone pairs of electrons that can be donated into the π-system of the benzene ring through resonance.

Ortho/Para Direction: This donation of electron density primarily increases the electron density at the ortho and para positions relative to the meta position. This makes the ortho and para positions more reactive than the meta position in the context of electrophilic substitution.

Analyzing Each Statement:

(A) \(Cl\) acts as an activating and \(o/p\) directing group.

The statement is incorrect. While \(Cl\) does direct substituents to the ortho and para positions due to its resonance effect, it is not an activating group overall. The inductive electron-withdrawing effect of chlorine dominates, making the ring less reactive to electrophiles, hence deactivating. Therefore, chlorine is a deactivating, \(o/p\) directing group.

(B) \(Cl\) acts as a deactivating and \(o/p\) directing group.

The statement is correct. Chlorine is deactivating due to its -I effect, which pulls electron density away from the ring, reducing its reactivity. However, due to its +R effect (resonance), chlorine increases electron density at the ortho and para positions, making these positions more reactive than the meta position. This means chlorine is ortho/para directing.

(C) \(Cl\) acts as an activating and \(m-\) directing group.

The statement is incorrect. This statement is incorrect on both counts. Chlorine is not activating; it’s deactivating. Moreover, it does not direct substitution to the meta position; it directs to the ortho and para positions.

(D) \(Cl\) acts as a deactivating and \(m-\) directing group.

The statement is incorrect. Chlorine is indeed a deactivating group, but it directs electrophilic substitution to the ortho and para positions, not to the meta position.

(E) Presence of \(NO_2\) at \(p-\) position facilitates the reactions.

The statement is correct. The \(NO_2\) group is a strong electron-withdrawing group (deactivating). When \(NO_2\) is present at the para position relative to the chlorine, it further withdraws electron density from the ring, especially stabilizing the intermediate carbocation formed during the electrophilic substitution reaction. This stabilization can make the reaction proceed more easily in certain conditions, thus facilitating the reaction.

Summary:

Chlorine (\(Cl\)) as a Deactivating, Ortho/Para Directing Group: The combination of chlorine’s -I effect (deactivating) and +R effect (ortho/para directing) means that while the ring overall is less reactive to electrophiles, when a substitution does occur, it will preferentially occur at the ortho or para positions relative to chlorine.

Nitro Group (\(NO_2\)) Facilitating the Reaction: The presence of a nitro group at the para position relative to chlorine further deactivates the ring by withdrawing electron density, which can stabilize the intermediate formed during the reaction, thereby facilitating certain reactions under the right conditions.

Thus, the correct answer is 4. B and E only.