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Topic: 1-2 Alkyl Shifts  (Read 1426 times)

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Offline MiuMixi

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1-2 Alkyl Shifts
« on: December 06, 2019, 01:00:48 AM »
When a carbonium ion adjacent to a quaternary carbon, but one of the branches is an ethyl or longer chain, can a 1,2 alkyl shift occur with that ethyl chain? Or is alkyl shift only limited to methyl groups

Offline sharbeldam

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Re: 1-2 Alkyl Shifts
« Reply #1 on: December 06, 2019, 02:09:47 AM »
If for instance you can a look at pinacol rearrangement, sometimes a Phenyl group can rearrange, so it's not limited, But I'd say it's easier/faster for hydrogen/methyl to migrate, Happy to be corrected if I'm wrong.
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Offline hollytara

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Re: 1-2 Alkyl Shifts
« Reply #2 on: December 06, 2019, 02:16:52 PM »
Other things being equal, the mass of the group makes a difference - lighter migrates faster.  But the difference in migration may create a mixture.  Phenyl migrates (the old 'phenonium ion' queation)...

If migration is coupled to other structural factors - changes in ring strain, for example - that can also change the preference.

Offline Babcock_Hall

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Re: 1-2 Alkyl Shifts
« Reply #3 on: December 06, 2019, 04:59:28 PM »
There are some examples in which a ring expands.  I recall seeing one in a textbook, in which a 5-membered ring became a six-membered ring.

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