Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: xshadow on June 01, 2021, 07:21:32 AM
-
Have a doubt:
If I have a ciclopentadiene and use 2eq NBS I'll get two bromination at the same allylic position or I get two bromination each one in a different allylic site
Thanks!!
-
Would you care to make a prediction and explain your reasoning?
-
Would you care to make a prediction and explain your reasoning?
After first cyclopentadiene allylic bromination I have:
- one allylic position with an Hydrogen and a bromine
- the other allylic position with two hydrogen
Now the second NBS equivalent could react with the allylic position already brominated or with the pther one
Now looking at the mechanism I get a radical when the C-H bond is cleaved by Br·
Now I don't know if I can say that a radical carbon is an electrophilic carbon and an halogen near it will destabilized that.
So the bromination will occour on the other allylic position where I don't have any halide
Another explanation is the steric hindrance
Br has a big steric hindrance and is hard for the second Br· to attack the allylic postion where is already bonded a Br
But I don't know if these explanations are good
Thanks....
-
I don't know the answer. However, I would argue that in some instances (bromination of alkanes), if there are steric effects, they are swamped out by relative stabilities of the radicals.
-
I dont understand, there is only one allylic site?
https://en.wikipedia.org/wiki/Cyclopentadiene
-
I dont understand, there is only one allylic site?
https://en.wikipedia.org/wiki/Cyclopentadiene
Sorry!!.my mistake
The molecule is cyclopentene
-
I think you get mainly one bromine in each site first then the tri and tetra bromo. But its really not easy to say, you have to do the experiment.
-
I think you get mainly one bromine in each site first then the tri and tetra bromo. But its really not easy to say, you have to do the experiment.
I thought that too..not so easy to predict
Thanks :)
-
I would look for the more stable radical.