Electrophilic Aromatic Substitution

In summary, the conversation discusses the major product formed in the nitration of compounds P, Q, and S using HNO3/H2SO4 mixture. It is determined that the answer will either be C or D, with P and Q having ortho substitution due to electron activating groups, and S having meta substitution due to the electron donating nature of the -OC=O group. The conversation concludes with a clarification that the -OC=O group is a +R group for the second benzene ring, promoting electrophile approach and ruling out the possibility of meta substitution.
  • #1
erisedk
374
7

Homework Statement


The compounds P, Q and S, were separately subjected to nitration using HNO3/H2SO4mixture. The major product formed in each case respectively, is :
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Homework Equations

The Attempt at a Solution


This is a standard EAS reaction. I know the answer will be either C or D, because in case of (P) -OH is more activating so the substitution will be with at ortho with respect to -OH (as para is blocked), similarly in case of (Q), it will be oath with respect to -OCH3 (more activating).
I don't understand what with respect to S. Is the -OC=O group electron withdrawing or donating? I thought it was withdrawing because the lone pair on oxygen is in resonance with the C=O bond (not with the benzene as the resonance with C=O is much more stable due to equivalent resonance structures (the reason why carboxylic acids are so stable). So, I thought the answer would be D and the substitution would occur at the meta position. But the answer is C. Help?
 
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  • #2
Though O might undergo resonance with Carbonyl carbon, it's still a +R group for the second benzene ring making it more electron Rich and promoting Electrophile approach
How would you justify meta position?
 
  • #3
Suraj M said:
Though O might undergo resonance with Carbonyl carbon, it's still a +R group for the second benzene ring making it more electron Rich and promoting Electrophile approach

Oh ok!
No meta then. I was thinking -I kind of thing. But got it!
 

1. What is electrophilic aromatic substitution?

Electrophilic aromatic substitution is a chemical reaction in which an electrophile (an electron-deficient atom or molecule) replaces a hydrogen atom on an aromatic ring.

2. How does electrophilic aromatic substitution occur?

Electrophilic aromatic substitution occurs through a two-step mechanism. In the first step, the electrophile attacks the aromatic ring, forming a short-lived intermediate. In the second step, a proton is transferred from the intermediate to reform the aromatic ring and create the substituted product.

3. What are the most common electrophiles used in electrophilic aromatic substitution?

The most common electrophiles used in electrophilic aromatic substitution are nitronium ion (NO2+), sulfur trioxide (SO3), and acyl halides (such as acetyl chloride).

4. What are the key factors that influence the rate of electrophilic aromatic substitution?

The key factors that influence the rate of electrophilic aromatic substitution include the strength of the electrophile, the nature of the substituent on the aromatic ring, and the stability of the intermediate formed during the reaction.

5. What are some examples of electrophilic aromatic substitution reactions?

Some common examples of electrophilic aromatic substitution reactions include the nitration of benzene to form nitrobenzene, the sulfonation of benzene to form benzenesulfonic acid, and the Friedel-Crafts acylation of benzene to form acetophenone.

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