1-buten+hydrogen bromide

[datdat]

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1-buten+hydrogen bromide in the presence of UV light...


isn't this reaction is just simple Markovnikove addition?

why is this a anti-Markovinkov? (kbb online midter Q.93) kbb said 'in the presence of peroxides..but there's no peroixdes, just UV light...if there's UV light do i have to consider it as peroxides?

confused...anyone can help me out?

 

[jrobb220]

Yea, it's a weird situation. uv light should do the same thing as a peroxide. they are both just activating a free radical reaction.

I thought i remembered from ochem a couple of years ago that HBr and light does anti, but most of the problems i have come across in the destroyer say it just does mark addition.

 

[NumbaOneStunna]

It's anti Mark.

 

[jrobb220]

yea
HBr/light or peroxide = Anti Mark
HCl/light or peroxide = Mark

 

[datdat]

yea
HBr/light or peroxide = Anti Mark
HCl/light or peroxide = Mark

what? HCl/peroxide is mark?

 

[bustedgrill]

what? HCl/peroxide is mark?

Think he mixed that up.

 

[UCB05]

In a normal markovnikov addition reaction, the double bond attacks a hydrogen to create a more substituted carbocation intermediate. Then the carbocation adds the nucleophile, resulting in the more substituted markovnikov product.

Peroxide and UV light catalyze free radical additions. The difference in mechanism is that the double bond attacks the bromide radical instead of a hydrogen ion to create a more substituted radical intermediate with the bromide now at the less substituted position. The reaction proceeds resulting in the less substituted anti-markovnikov product.

The reaction mechanism leading to the more substituted cation/radical intermediate is what causes the mark/anti-mark difference. It's important to understand that and it makes much more sense to me when I think about it in terms of intermediate formation.

I've read in Destroyer that HCl + peroxide/UV adds markovnikov because Cl radical is much less selective. I'm of the opinion that due to HCl radical formation being endothermic, this type of reaction generally does not occur.

 

[solstice]

Think he mixed that up.

No he DID NOT.

HCl react as usual. ONLY Bromium is affected.

 

[bustedgrill]

No he DID NOT.

HCl react as usual. ONLY Bromium is affected.

Okay, so HCl/H2O2 will give you mark? could you explain this a wee bit more please?

 

[jrobb220]

can't explain it, just know it.