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Author Topic: Arylic vs benzylic carbocation  (Read 604 times)

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owlpower

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Arylic vs benzylic carbocation
« on: October 12, 2018, 06:03:35 AM »

For the first addition reaction, when the curly arrow goes from the pi bond to the H atom, I wonder where to place the H atom as both sides of the alkene have 1H attached. I am not sure whether an arylic or benzylic carbocation is more stable.

For the second addition reaction, there should be 2 products as the Br can attack from both top and bottom (stereoselectivity), resulting in enantiomers, right? (But when I've drawn them, I've got the R,S product only...)
« Last Edit: October 12, 2018, 06:22:25 AM by owlpower »
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mjc123

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Re: Arylic vs benzylic carbocation
« Reply #1 on: October 12, 2018, 06:36:16 AM »

Reaction 1 can give 2 carbocations one of which is resonance-stabilised and the other not. How are you unsure which is more stable?

Reaction 2: whichever side initial attack comes from, the product must have the two Br atoms on opposite sides of the plane of the molecule as drawn. There are two asymmetric carbons, and you can get R,S' or S,R' (enantiomers), but not their diastereomers R,R' and S,S'.
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owlpower

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Re: Arylic vs benzylic carbocation
« Reply #2 on: October 12, 2018, 09:57:30 PM »

Is the first reaction like this?
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