Do radicals rearrange?

[sfoksn]

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Do radicals rearrange like carbocation?

For example, if you were to react 2-methyl-3-hexene with HBr in ROOR, then would the radical formed rearrange to form tertiary radical?

If they do rearrange, what are the circumstances?

 

[RCT PC CRN]

I'm not certain but this is how far my ochem knowledge will take me.

I don't think radicals rearrange. Where there is possible to form 2 or more radicals you will have mix of products where most stable radical intermediate will form major product.

I just cann't picture e moving around with radicals.

I would love to see more certain responses.

 

[UndergradGuy7]

Do radicals rearrange like carbocation?

For example, if you were to react 2-methyl-3-hexene with HBr in ROOR, then would the radical formed rearrange to form tertiary radical?

If they do rearrange, what are the circumstances?

I don't remember them re-arranging. I think there is some rare time they do, but we never talked about it in organic chem. And I think we are supposed to assume they don't in our organic classes.

Anyone else?

 

[sfoksn]

I thought not, but just confirming.

Another thing, its only HBr that adds anti mark with ROOR, right? If we had HCl or HF, then whether or not we have ROOR, it will always add mark, correct?

Also, when we have Br2 and adding stuff to alkane through radicals, then it is controlled, and when we have Cl2/F2 and adding stuff to alkane through radical, then it isn't controlled?

Just trying to refresh my memory 🙂

 

[Baylor2011]

What are you indicating by ROOR.. like Me - O - O - Me? As far as I know the only things that add antimarkovnikov are HBr in peroxides as well as Diborane.

 

[dshope]

I remember seeing similar question in a orgo book

like carbocations radicals can rearrange themselves to become more stable (tertiary > secondary > primary)

however the main difference is in carbocation rearrangement, even the methyl group can be moved around for more stable structure, this is not the case with radicals
the radical can rearrange themself but the methyl group will not move

 

[UCB05]

I thought not, but just confirming.

Another thing, its only HBr that adds anti mark with ROOR, right? If we had HCl or HF, then whether or not we have ROOR, it will always add mark, correct?

Also, when we have Br2 and adding stuff to alkane through radicals, then it is controlled, and when we have Cl2/F2 and adding stuff to alkane through radical, then it isn't controlled?

Just trying to refresh my memory 🙂

HBr radical addition is the only relevant one. It's the only hydrogen halide whose radical addition reaction is favorable in all intermediate reactions. All the other HX's have some endergonic step in initiation, propagation, or termination.

What are you indicating by ROOR.. like Me - O - O - Me? As far as I know the only things that add antimarkovnikov are HBr in peroxides as well as Diborane.

ROOR is a peroxide 😉

 

[Baylor2011]

haha, ok thanks. that was completely throwing me off.

 

[sfoksn]

So, radicals do arrange themselves? And can anyone confirm what I said about radical addition of halogen with alkanes?

Thanks 🙂

 

[wantVCUdental]

I'm not certain but this is how far my ochem knowledge will take me.

I don't think radicals rearrange. Where there is possible to form 2 or more radicals you will have mix of products where most stable radical intermediate will form major product.

I just cann't picture e moving around with radicals.

I would love to see more certain responses.

Radicals DO REARRANGE themselves! And the most incorrect assumption is that you are picturing 1 electron at a time. Electron placements around a molecule is all hypothetical... in actuality, electrons form a cloud which disperse its orbit/energy over the existing nuclei. The fact that you form multiple product/forms of intermediate is due to the propensity of an electron to exist in one area over another (this in itself is driven by an equilibrium). And when mixed products of radicals form, those do not always form in equal proportions because some intermediates are more stable than others. And if the molecule is able to achieve a lower energy transition state through rearrangement, IT WILL.
Hope that helps.