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Confused about organic question


azazel2113
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Hi there, I have a question about a question. in the picture I have attached, the question says that the alkene undergoes hydrobromination. However, to me, the reaction given looks like a halogenation, not a hydrohalogenation. I was wandering if I am correct in thinking that or if I am missing something.

 

Thank you

post-62326-0-22210000-1323031652_thumb.jpg

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Firstly, why don't you draw out the structures that you think you would get if it was a bromination.

 

A hydrobromination is a specific type of halogenation (since bromine is a halogen). What do you get if you treat an alkene with bromine?

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Sorry about the size of my writing haha. Took the picture with my camera phone.

 

As far as where the H comes from, that is what is really confusing me. The next question actually asks to draw the mechanism of the most stable, which I believe is the first picture. However, I cannot figure out how to go from Br2 to HBr. Do you have any suggestions?

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Correct. Are you familiar with the mechanism for di-brominations with Br2? It is said to go via a cyclic bromonium ion intermediate, like this:

 

(Image from here)

 

Ignore the image I got from there and that was sitting right here where you're reading, as it's been deemed inaccurate. See this post for an updated mechanism.

Which means that you will really only get 1,2-dibromination.

 

I am slightly confused as to why the questions states it is a hydrobromination, though. There's clearly no proton source in your reaction, so that isn't going to happen (unless I'm missing something).

Edited by hypervalent_iodine
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Alright, sunshine, we get it and we were just poking fun. I happen to agree with you, I just missed it when going through and getting pictures. Anyway, problem solved and I'm sure the OP understands that there is an arrow in there that wasn't drawn in by the author. But heck, for the sake of accuracy:

 

bromination-2-1.jpg

 

 

I even included the partial charges; just for you, Horza. Can't have you being any more disappointed in me, now can we? :P

Edited by hypervalent_iodine
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You've still got it wrong.

 

Yeah thats it. Otherwise the cyclic bromonium intermediate never happens.

 

Without that cyclic flow of electrons there is also a parity violation I believe.

 

We just had to give you some hell Horza for leaving us Horza-less for so long. Good to have you back at the metaphorical hood.

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You know it's bad when you wake up in the morning and the first sinking feeling you think is, 'Ah, crap, I forgot an arrow and why the hell did I post that at 2.23am'?

 

Welcome back, Horza.

 

Anyway, I have no idea what you're talking about, if you'll see, my mechanism is totally correct and I absolutely did not go and fix it and edit my post accordingly.

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