Question about EAS...

[PocketRocket]

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Would an e- withdrawing group on a benzene speed up the addition of an e-donating group just like an e-donating group on a benzene would speed up the addition of an e-withdrawing group?.......or is it just that the presence of an e-donating group will indefinitely speed up the addition of any group since it is an electrophile that we are adding?

I hope that made sense, thanks

 

[DAT Destroyer]

Would an e- withdrawing group on a benzene speed up the addition of an e-donating group just like an e-donating group on a benzene would speed up the addition of an e-withdrawing group?.......or is it just that the presence of an e-donating group will indefinitely speed up the addition of any group since it is an electrophile that we are adding?

I hope that made sense, thanks

An electron-withdrawing group will slow down a reaction assuming it is an Electrophilic Aromatic Substitution. For example......if a Methoxy group or Hydroxy group was on a benzene ring.....it is quite activating.......introduction of a Nitro group would slow it down......however....as always, the activating group will do the directing.

Hope this helps.

Dr. Romano

 

[PocketRocket]

An electron-withdrawing group will slow down a reaction assuming it is an Electrophilic Aromatic Substitution. For example......if a Methoxy group or Hydroxy group was on a benzene ring.....it is quite activating.......introduction of a Nitro group would slow it down......however....as always, the activating group will do the directing.

Hope this helps.

Dr. Romano

And this is irrespective of the kind of group the electrophile will become?

 

[DAT Destroyer]

And this is irrespective of the kind of group the electrophile will become?

You need to give me a specific example......the original question was not clear.

Thanks
Dr. Romano

 

[mgc]

I think what he/she is asking is that suppose you have benzene with a strong EWG (deactivator) such as a nitro. Now suppose the reagent to be added is a EDG that will activate the ring once it has been added to the ring - will this speed up the rxn?

I believe the answer is no. The presence of a group that might become an EDG on ring, will not speed up a reaction. An EWG deactivates a ring by withdrawing electron density from the ring and thus, making it less reactive to EAS. The speed of reaction will be in the order of: Ring with EDG (Activated) > Benzene > Ring with EWG (Deactivated).

 

[DAT Destroyer]

I think what he/she is asking is that suppose you have benzene with a strong EWG (deactivator) such as a nitro. Now suppose the reagent to be added is a EDG that will activate the ring once it has been added to the ring - will this speed up the rxn?

I believe the answer is no. The presence of a group that might become an EDG on ring, will not speed up a reaction. An EWG deactivates a ring by withdrawing electron density from the ring and thus, making it less reactive to EAS. The speed of reaction will be in the order of: Ring with EDG (Activated) > Benzene > Ring with EWG (Deactivated).

Well done!

Dr. Romano