Group shift sn1 or e1 e2?

[magdi1989]

Im really confused on when do we shift groups in organic chemistry reactions.....

Do we only shift in SN1 or can we also shift in E1 E2?

THANKS

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[ename1]

There can be shifts in SN1 and E1, because they involve carbocation intermediates.

 

[magdi1989]

There can be shifts in SN1 and E1, because they involve carbocation intermediates.

Ok but how do i know when to do a shift. Because i get confused when i do a reaction. Can you give me some examples please.

Thanks

 

[ename1]

"Shifts" or Rearrangements occur when a more stable carbocation can be formed as a result of a rearrangement. Stability of carbocations is as follows:

Third degree carbocations are more stable than second degree which are more stable that first degree.

An example: if you have 2-bromo-3-methyl butane and the Br leaves, it results in a second degree carbocation (two carbons bonded to the positively charged carbon). A third degree carbocation is more stable, so a hydride shift will happen and leave a positively charged carbon bound to 3 other carbons, making the molecule more stable.

Hope this helps, seems a little wordy.

 

[magdi1989]

"Shifts" or Rearrangements occur when a more stable carbocation can be formed as a result of a rearrangement. Stability of carbocations is as follows:

Third degree carbocations are more stable than second degree which are more stable that first degree.

An example: if you have 2-bromo-3-methyl butane and the Br leaves, it results in a second degree carbocation (two carbons bonded to the positively charged carbon). A third degree carbocation is more stable, so a hydride shift will happen and leave a positively charged carbon bound to 3 other carbons, making the molecule more stable.

Hope this helps, seems a little wordy.

Thanks.

Now only a hydrogen can shift right?

 

[PreDent11]

Thanks.

Now only a hydrogen can shift right?

There can be methyl shifts as well.

 

[wall1two]

how many carbons could a methyl shift?

if i had 5-ido 2-methyl octane would my methly shift the 3 carbons? or does my cation shift down to number 2, or would i just have e1/sn1 at the spot?

 

[ename1]

I have only seen a methyl group shift from an adjacent carbon

 

[recyrb]

ename- in your example, does only the Hydrogen shift from carbon 3 to carbon 2 ? stablizing the secondary C-2 and leaving c-3 with the positive charge?

 

[ename1]

ename- in your example, does only the Hydrogen shift from carbon 3 to carbon 2 ? stablizing the secondary C-2 and leaving c-3 with the positive charge?

Yes that is correct.

 

[invictusx]

I have only seen a methyl group shift from an adjacent carbon

Ditto