Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: MiuMixi on December 06, 2019, 01:00:48 AM
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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
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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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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.
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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.