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I'm studying organic chemistry at the moment and it's really confusing. What could ever happen between benzene and an alkene? and why is $\ce{H2SO4}$ there?

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Sulfuric acid protonates the alkene to give the highest substituted carbocation, tert-butyl. That electrophilically adds to a benzene carbon atom, to give the obvious next cation. A proton is eliminated to obtain tert-butylbenzene. Akyl groups activate benzene rings toward ortho, para attack (mild electron donation via hyperconjugation), thus 1,6-di-tert-butylbenzene, certainly if the addend is in excess. Especially stable carbocations can dissociate and wander around the benzene ring under Friedel-Crafts conditions. If you push it, you get 1,3,5-tri-tert-butylbenzene.

Steric hindrance strongly discourages further reaction. You can go to the literature to find how many adjacent tert-butyls can be jammed onto a benzene ring - and how it is done.

With due respect, you are in deep trouble for passing the course if the Friedel-Crafts reaction throws you. Either look at things with the LCAO model, look in a few more textbooks, or talk with folks who have grasped it. You must understand it. You cannot survive substituent effects if you cannot flip bonds. This is easy stuff compared to what will follow. Chess can be well-played by computer. Organic synthesis is done in wetware, though computers help help.

http://www.chemtube3d.com/model/electrophilic_aromatic_substitution/friedel-crafts/alkylation/benzene%2Btbu/mechanism.png
Close enough

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First, I think the name of your molecule must be malformed. That said, the reaction of an alkene with strong acid can generate a carbocation. That carbocation is electrophilic, and can react with benzene (as the nucleophile) in an electrophilic aromatic substitution reaction. The final product is the (potentially poly-)alkylated benzene.

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  • $\begingroup$ THANKS FOR ANSWERING! which molecule is wrong? I typed what it said, or showed an an ethylene molecule with two methyls hanging off of it, and H2S04 is also in the equation maybe as a catalyst I dont know, so just want to clarify the benzene dosent open up any of its double bonds right? its just the ethylene and it opens up creating the carbo cation right? $\endgroup$ – Unistudent9 Nov 5 '13 at 22:32
  • $\begingroup$ @Unistudent9, if I understood you correctly, the alkene you're referring to is one of the isomers of 2-butene. The benzene does not react directly with the acid. Rather, the proton transfer to the 2-butene produces a carbocation, which is attacked by the benzene, resulting in alkylation of the benzene ring. Look up electrophilic aromatic substitution for a detailed mechanism. $\endgroup$ – Greg E. Nov 6 '13 at 6:19
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I took the liberty and corrected the title of your question, assuming that the "ethylene with two methyls" is 2-methylpropene (isobutene). Over here, this classic reaction is known as Friedel-Crafts alkylation.

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