thelonious
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friedel-crafts mechanism
I have a very noobish question.
http://gyazo.com/c5f3811610aaf65446a902e7576fc082.png?135495...
In the above picture, mechanism 1 is the Friedel-Crafts mechanism as I know it.
Why doesn't mechanism 2 happen? Wouldn't it be more likely that the strongly nucleophilic chlorine on AlCl4- would attack the
strongly electrophilic carbocation on the benzene ring, rather than the weakly nucleophilic hydrogen?
I know that the second product lacks the resonance stabilization of the first one, but I even then, it seems to me that at least some of the second
product should form.
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sargent1015
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Well, for one, as pictured, you have gotten rid of the stable conjugated pi system (the benzene ring) which is highly unfavorable. This is the big
thing here. Don't wreck your aromatics! It doesn't happen (easily).
Also, chlorine is by far one of the worst electrophiles of all. Just sayin. Better leaving group than anything.
Hope that helped!
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thelonious
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Quote: Originally posted by sargent1015  | Well, for one, as pictured, you have gotten rid of the stable conjugated pi system (the benzene ring) which is highly unfavorable. This is the big
thing here. Don't wreck your aromatics! It doesn't happen (easily).
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Ok, due to the stability of the pi-conjugated system, the first product is favoured, that makes sense. Thank you!
I don't think I understand what you mean, isn't chlorine acting as a nucleophile here, not an electrophile?
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sargent1015
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I think I said that wrong, can anyone correct me on that nomenclature? Either way, chlorine does not to a good job binding to compounds of this sort
and is a much better leaving group than anything else. There are exceptions of course, but in general, chlorine does not readily react in this
fashion.
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