Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: chrisbb on October 07, 2010, 04:50:31 PM
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Hi everyone.
I'm trying to understand this mechanism and the R/S configurations for my lab.... not trying to just write down the answer given to us.
Here is what I have:
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi54.tinypic.com%2Fojjour.jpg&hash=480085d5f1c773a5e0be7de7118e01e3d06dc9d6)
So.
I chose that the bromine attacks from the top, creating a Bromonium ion. The next Br- comes in from the BOTTOM, because the first bromine takes up too much room. The top bromine would be pointing up, and then bottom one point down....
Is that correct?
I understand how to write R/S configurations, but I don't think that the mechanism is correct, due to the fact that I'm getting two S configurations....
I'm a little confused as to the right hand carbon.... what did I do wrong to get 2 R's??
Thanks.
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learnt a lot from your mechanism. nicely written. thanks.
two things i would like to point out: attack of bromine and R/S configuration.
1. If you choose to attack the bromine from the bottom, you will get the other enantiomer i believe.
I find no problems with both carbons being in the same configuration in the final structure.
2. I think the carbon bonded to bromine (i.e. the -CHBrPh group) has got more priority than the phenyl group (1st point of difference); Ph would be number 3 and both would be R instead of S in the structure you have drawn. conversely, both would be S in the other enantiomer.
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I draw a picture to help chrisbb understand this mechanism . I used Fischer projection in the picture ,if you don't know what is it or how use it ,you may need this :
http://en.wikipedia.org/wiki/Fischer_projection
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amazing diagram!
Thank you! Yes I understand the Fisher Projections! :)
Question still though.
When looking at each chrial center, I list the priorities as:
1) Br
2) Phenyl
3) R-group
4) H
Am I correct in doing so for my diagram?
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the priorities :
Br
C-Br
Ph
H
I think this is where you confused.
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thanks, yes it turns out that I forgot that the right hand carbon was the wrong configuration.
Every time I looking, both hydrogen's came OUT the page, when one should be in and the other out.
Thanks for all your help :)