[xshadow]

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!!

[Babcock_Hall]

Would you care to make a prediction and explain your reasoning?

[xshadow]

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....

[Babcock_Hall]

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.

[rolnor]

I dont understand, there is only one allylic site?
https://en.wikipedia.org/wiki/Cyclopentadiene

[xshadow]

I dont understand, there is only one allylic site?
https://en.wikipedia.org/wiki/Cyclopentadiene

Sorry!!.my mistake
The molecule  is cyclopentene

[rolnor]

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.

[xshadow]

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

[Babcock_Hall]

I would look for the more stable radical.