Bromine???

[utdent20]

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Ok I am taking the beast in 5 days.. count down begins.
I amg etting confused in the addition of Br in its different ways. I have the markinkoff and anti markinkoff rule down but what is getting me is when do i know that there we an addition of
1.2 Br's as in 2 individual Br's area added to the molecule via Cold Br2?
2. Br2/FeBr3---->? One Br or two?
3.Br.ROOR---> Anti ?? right
4.BrNBS---> markinkoff?
5. Br/CCl4---> 2 br's
6. are they any others we need to know?

 

[alex dds]

Ok I am taking the beast in 5 days.. count down begins.
I amg etting confused in the addition of Br in its different ways. I have the markinkoff and anti markinkoff rule down but what is getting me is when do i know that there we an addition of
1.2 Br's as in 2 individual Br's area added to the molecule via Cold Br2?
2. Br2/FeBr3---->? One Br or two?
3.Br.ROOR---> Anti ?? right
4.BrNBS---> markinkoff?
5. Br/CCl4---> 2 br's
6. are they any others we need to know?

2. Bromination as in EAS? Then One Br.
3. HBr/hv or ROOR -> Anti Mark
4. Br/NBS -> I believe that's Mark (correct me if I'm wrong)
5. Br/CCl4 -> 2 Br's anti addition
6. Br2/hv -> adds to most stable carbocation
7. 1) BH3, THF/ 2) H2O2, OH- -> For me, I would always think it adds OH anti-Mark (Again correct me if I'm wrong)

Any others? 😕

 

[utdent20]

2. Bromination as in EAS?what is EAS? Then One Br.
3. HBr/hv or ROOR -> Anti Mark
4. Br/NBS -> I believe that's Mark (correct me if I'm wrong)that is right
5. Br/CCl4 -> 2 Br's anti addition anti is correct.
6. Br2/hv -> adds to most stable carbocation.right.
7. 1) BH3, THF/ 2) H2O2, OH- -> For me, I would always think it adds OH anti-Mark (Again correct me if I'm wrong) I always think H2O2 means going to the least subsitutted. Now BH3 THF i thought we get an OH in a diff plane than the orignal molecule.. I think.

that is all i can think of. THanks!

 

[alex dds]

EAS is elecrophilic aromatic substitution, so when you add Br2/FeBr3, you add one Br to the Benzene ring. 👍

 

[gentile1225]

Br/NBS and Br/hv act the same way, yes it is anti, but remember if you have a benzene ring, you must have a benzylic hydrogen to pluck off and replace when using NBS

 

[utdent20]

Br/hv i thought was markinkoff going to the most subsituted..though.. and anti was in ROOR

 

[gentile1225]

you are right im sorry. roor is anti, but nbs/roor is especially efficient in pulling off a benzyllic hydrogen and replacing it with a bromine. if there is a benzene ring with a benzyllic hydrogen im pretty sure br2/hv will do the same thing.