Orgo road map

[jdent]

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I'm missing something here. On one of the road maps 1-methyl-cyclohexene plus Br2 in H2O gives product with OH on same carbon as the methyl group and OH is on carbon number 2. Now Br is higher priority then OH. If so then shouldn't Br attach to same carbon as the methyl group?

 

[Mstoothlady2012]

I'm missing something here. On one of the road maps 1-methyl-cyclohexene plus Br2 in H2O gives product with OH on same carbon as the methyl group and OH is on carbon number 2. Now Br is higher priority then OH. If so then shouldn't Br attach to same carbon as the methyl group?

This doesn't make sense to me. Do you mean the second carbon has Br?

 

[jdent]

yes. Carbon number one which is more substituted has the methyl and OH and carbon number 2 has the BR.

 

[klutzy1987]

I'm missing something here. On one of the road maps 1-methyl-cyclohexene plus Br2 in H2O gives product with OH on same carbon as the methyl group and OH is on carbon number 2. Now Br is higher priority then OH. If so then shouldn't Br attach to same carbon as the methyl group?

The way it works is that the Br takes the place of the that an H would take in a standard Oxymercuration reaction. Therefore the Br goes to the Carbon that has more Hydrogens and the OH will still go to the most substituted carbon.

 

[jdent]

Thanks but why? Br is higher ranking than the OH?

 

[Mstoothlady2012]

The way it works is that the Br takes the place of the that an H would take in a standard Oxymercuration reaction. Therefore the Br goes to the Carbon that has more Hydrogens and the OH will still go to the most substituted carbon.

This is not oxymercuration reaciton

 

[klutzy1987]

Thanks but why? Br is higher ranking than the OH?

But remember how that mechanism works, First Br attacks and then OH therefore you want the carbocation to be the most stable. I belive that is the correct reason.

 

[jdent]

But remember how that mechanism works, First Br attacks and then OH therefore you want the carbocation to be the most stable. I belive that is the correct reason.

Ah! I hear, since Br attacks first then you got the carbocation so then the OH will attack to stabilize the carbocation. Thanks! Really appreciate you coming on DAT discussion to help fellow DESTROYER guys even though you finished your DAT. 🙂

 

[Mstoothlady2012]

But remember how that mechanism works, First Br attacks and then OH therefore you want the carbocation to be the most stable. I belive that is the correct reason.

eventhough your reasoning makes sense, but there is no carbocation formation with Br2 addition. There is bromonium ion intermediate, but no carbocation.

 

[klutzy1987]

eventhough your reasoning makes sense, but there is no carbocation formation with Br2 addition. There is bromonium ion intermediate, but no carbocation.

Yes but here you are not adding Br2 you are adding Br2/H2O to get a halogen alcohol. It is a different mechanism than a standard double halogenation. Correct me if i am wrong but i believe that there would be a carbocation intermediate in this reaction.

 

[jdent]

I think Klutzy is right!

 

[Mstoothlady2012]

Yes but here you are not adding Br2 you are adding Br2/H2O to get a halogen alcohol. It is a different mechanism than a standard double halogenation. Correct me if i am wrong but i believe that there would be a carbocation intermediate in this reaction.

I am looking at my orgo book and it has the mechanism of Br2/H2O and it shows no carbocation formation. The reason that you gave was the first reason I thought of until I looked at this mechanism.

 

[Mstoothlady2012]

Here is the mechanism I found online, which has the same mechanism as my book. It also says that C-O bond forms at more stable caiton. But there is no carbocation!!! lol

http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch06/ch6-8.html

 

[Mstoothlady2012]

And its SN2 like so it should attack the secondary carbon rather than tertiary lol its going against all the rules.

 

[Mstoothlady2012]

See attachment

phew finally figured it out 😀

 

[jdent]

I see what your saying thanks for the reference. One question thats by Cl but what about Br. I know your going to say that they are both halides. But you should know that there are cases where it isn't. Br is specific and will only react with tertiary while Cl will even react with secondary.

 

[WayneSU]

See attachment

phew finally figured it out 😀

in the halonium ring, its bromine that is carryin a postive charge.....r the carbons also carrying a partial positive charge?

 

[Mstoothlady2012]

I see what your saying thanks for the reference. One question thats by Cl but what about Br. I know your going to say that they are both halides. But you should know that there are cases where it isn't. Br is specific and will only react with tertiary while Cl will even react with secondary.

I have no idea what you are talking about. In this case both Br & Cl react equally. Br2 & Cl2 addition undergo same mechanism. I2 & F2 are not reactive.

Br & Cl differ when we are using ROOR

 

[Mstoothlady2012]

in the halonium ring, its bromine that is carryin a postive charge.....r the carbons also carrying a partial positive charge?

apparently yes! I guess they have partial positive charge b/c of Br 😕