chemist1243
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do benzene substitutents have any effect on the outcome of a FC akylation?
do benzene substitutents have any effect on the outcome of a FC alkylation?
i would imagine if you tried to alkylate say, methoxy benzene, maybe steric hinderence would come into play and prevent poly alkylation? or at the
very least slow the rate at which poly alkylation would occur? what kind of yeilds could be expected from this compared to FC alkylation of plain old
benzene?
a second opinion on this would be apreciated.
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DavidJR
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Yes, the substituents do affect the rate of any kind of electrophilic aromatic substitution (which includes Friedel-Crafts alkylation).
Activating groups increase the electron density on the ring, making the ring more nucleophilic and therefore more reactive towards electrophiles.
Deactivating groups do the opposite. In fact, alkyl groups are weakly activating, which is why FC alkylations are so prone to multiple alkylation.
Substituents also affect which positions on the ring are more reactive in the context of EAS. These can be put into two categories: ortho/para
directing, and meta directing. Activating groups are all ortho/para directing, and deactivating groups are mostly meta directing with the exception of
halo and nitroso groups.
Lastly, steric hinderance will always be a factor but it is really only significant when the substituent is big and bulky (e.g. tert-butyl).
Reading material: https://en.wikipedia.org/wiki/Electrophilic_aromatic_directi... and https://www.masterorganicchemistry.com/2017/09/26/activating...
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chemist1243
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Quote: Originally posted by DavidJR  | Yes, the substituents do affect the rate of any kind of electrophilic aromatic substitution (which includes Friedel-Crafts alkylation).
Activating groups increase the electron density on the ring, making the ring more nucleophilic and therefore more reactive towards electrophiles.
Deactivating groups do the opposite. In fact, alkyl groups are weakly activating, which is why FC alkylations are so prone to multiple alkylation.
Substituents also affect which positions on the ring are more reactive in the context of EAS. These can be put into two categories: ortho/para
directing, and meta directing. Activating groups are all ortho/para directing, and deactivating groups are mostly meta directing with the exception of
halo and nitroso groups.
Lastly, steric hinderance will always be a factor but it is really only significant when the substituent is big and bulky (e.g. tert-butyl).
Reading material: https://en.wikipedia.org/wiki/Electrophilic_aromatic_directi... and https://www.masterorganicchemistry.com/2017/09/26/activating... |
okay thank you. this is very helpful.
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B(a)P
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Give this a watch https://youtu.be/6ydPCBEVjXY
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