Questions about Benzene: Substituent Effects & -Cl Group

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Discussion Overview

The discussion revolves around the effects of substituents on a benzene ring, specifically focusing on the -Cl group and its role as an electron donating or withdrawing group. Participants explore the implications of these effects on the reactivity and directing nature of substituents in electrophilic aromatic substitution (EAS) reactions.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why the -Cl group is considered electron donating, suggesting it may pull delocalized electrons and stabilize the ring.
  • Another participant clarifies that halogens can donate electrons through resonance while withdrawing them through induction, noting that Cl's inductive effect is stronger, making it a deactivating substituent overall.
  • A different participant points out that despite being a deactivating substituent, -Cl is ortho/para directing due to the ability to form a resonance-stabilized intermediate during the reaction mechanism.
  • Another participant emphasizes that not all ortho-para directors are equally activating, using the methyl group as a comparison, and suggests that chlorine's electron donation is limited and context-dependent.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the -Cl group as an electron donating or withdrawing substituent, leading to an unresolved discussion regarding its overall effects on benzene reactivity and directing behavior.

Contextual Notes

The discussion reflects varying interpretations of the electronic effects of substituents, particularly the balance between resonance and inductive effects, which may depend on specific reaction conditions or contexts.

kanki
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I have some questions here about Benzene.
So the presence of one substituent in a benzene ring will affect the ease and position of any further substituent group, such like [itex]-CH_3,NO_2,Cl[/itex].
And it's known that the Ortho,para-directing groups or electron donating groups are ring activating, consists of single bond, and will make the benzene ring easier to be attacked.
My question is, why is it that the -Cl group is electron donating? i thought it'll pull the delocalised electron in the ring and stabilise it?
 
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kanki said:
I have some questions here about Benzene.
So the presence of one substituent in a benzene ring will affect the ease and position of any further substituent group, such like [itex]-CH_3,NO_2,Cl[/itex].
And it's known that the Ortho,para-directing groups or electron donating groups are ring activating, consists of single bond, and will make the benzene ring easier to be attacked.
My question is, why is it that the -Cl group is electron donating? i thought it'll pull the delocalised electron in the ring and stabilise it?

Halogens donate electrons by resonance, and withdraw electrons by induction through the bond. However, Cl's inductive withdrawing is stronger than its resonance donation, so it is overall a deactivating substituent for reactivity in EAS.
 
Last edited:
So it is overall a deactivating substituent, and render the benzene ring unreactive. But why is it Ortho-para directing? Please explain...
 
The ortho/para directing is observed because you can draw a resonance stabilized intermediate in the mechanism.
 
And it's known that the Ortho,para-directing groups or electron donating groups are ring activating, consists of single bond, and will make the benzene ring easier to be attacked.
My question is, why is it that the -Cl group is electron donating? i thought it'll pull the delocalised electron in the ring and stabilise it?

you should re-read your text, from what I remember, not all ortho-para directors are so activating as a methyl group is for example. Chlorine's electrons are donating to a degree since it is delocalized to an extent.
 

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