Organic question Radical bromination

[Hokie08]

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In question 99 of topscore it says in radical bromination the free radical forms the most stable carbocation for the Br to attach to. I always thought radicals always are added anti-markovnikov? Also in the destroyer roadmaps I see in road map 3 Br2, hv is added to the allylic carbon but in roadmap 3 it attaches the same carbon as the methyl group.....can anyone explain this? Thanks

 

[Decan]

Which methyl group are you talking about? Br adds to c1 og methylcyclopentane b/c it will form a tertiary radical. Up top, it adds to the double bonds because you react HBr with ROOR, which causes it to add anti-markovnikov. Adding HBr without ROOR would gaive you 1 bromo 1 methyl cyclopentane.

Hope that helps.

 

[quikag1]

The only time that you have anti-markovnikov will be when you use HBr and ROOR(peroxide) or if you do hydroboration oxidation ( which also has a peroxide) otherwise you add the hydrogen ( or whatever else you are using depending on the rxn) to create the most stable radical or carbocation. Make sure to memorize the stability order for carbocations and radicals to avoid making an error! (they are in any orgo book). The allylic radical/carbocation is stabilized by resonance and thus will form easily. Roadmap #3 in the destroyer depicts this rul very clearly. When Br2/hv or HBr added, you form the most stable radical or carbocation ( in this case it was the tertiary carbocation that would be created by the methyl group attached to C-1. But if you have a 2X bond and you use HBr with ROOR it adds Br anti markovnikov as shown.
Hope this helps. This stuff is crucial so make sure you understand it well before going on.
Good luck

 

[PD3]

Where in the Destroyer are these roadmaps people speak of?

 

[Decan]

The roadmaps are in the solutions section

 

[Dentalicous1234]

In question 99 of topscore it says in radical bromination the free radical forms the most stable carbocation for the Br to attach to. I always thought radicals always are added anti-markovnikov? Also in the destroyer roadmaps I see in road map 3 Br2, hv is added to the allylic carbon but in roadmap 3 it attaches the same carbon as the methyl group.....can anyone explain this? Thanks

I'm having the same problem. I understand there's a difference b/t using HBr and peroxide (anti markovnikov) and Br & hv BUT what is the rule for Br and hv? In destroyer roadmap 2 it adds to the carbon not in the ring but in roadmap 3 it adds to the carbon in the ring(same carbon as the methl group).

In roadmap 2 this is the bottom left hand corner Br hv addition and in roadmap 3 it's the first ones if you start at the "start" product.

doesn't Br with hv mean you get Br radicals? aren't radicals always anti-markovnikov?

 

[Sillygirl]

Nope they don't always add Anti-Markovnikov. They add to produce the most stable radical and that's the one thats going to be on the highest substituted carbon. I thought at first they always added Anti-Markovnikov too. I blame Kaplan.

 

[Dentalicous1234]

Nope they don't always add Anti-Markovnikov. They add to produce the most stable radical and that's the one thats going to be on the highest substituted carbon. I thought at first they always added Anti-Markovnikov too. I blame Kaplan.

thanks for responding i'm glad someone else noticed this issue too cuz YEA! kaplan says everywhere that it is anti and destroyer sometimes has it not anti so i'm getting soooo confused!
so then if it isn't always anti, when is it and when is it not? 😕
When you add it to an alkene it is anti but if its just an alkane its not anti?
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