About Benzene

  • Thread starter 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.
 
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So it is overall a deactivating substituent, and render the benzene ring unreactive. But why is it Ortho-para directing? Please explain...
 

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The ortho/para directing is observed because you can draw a resonance stabilized intermediate in the mechanism.
 

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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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