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Elimination of 3-methyl-butan-2-ol

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in Organic Chemistry

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Hi everyone

 

Asked is to give all possible elimination products after elimination of 3-methyl-butan-2-ol in a sulfuric-acidic/water environment.

 

The answer would be:

  • (mostly) 2-methyl-but-2-ene
  • (a bit) 3-methyl-but-1-ene

Why can't 2-methyl-but-1-ene be formed? It's not like the second possibility is conform Zaitsev's rule so... Why not 2-methyl-but-1-ene?

 

Thanks!

 

F.

  • 3 months later...

Hello there,

 

Actually, your 2-methyl-but-1-ene is labeled incorrectly. The double bond gets priority, so it should be 3-methyl-1-butene.

 

To answer your question, since this is an elimination reaction, we have to consider beta hydrogens. The major product (2-methyl-but-2-ene) would be formed moreso over the 3-methyl-1-butene. This is because if the reaction proceeded as a carbocation, the tertiary carbon is more stable, hence creating a major product of 2-methyl-but-2-ene. The minor product is only a small yield because upon elimination of a beta hydrogen, a secondary carbocation would be formed (the relative reactivity of carbocations are 3>2>1.

 

It's not that the minor product is not formed at all, but it would be in a small amount compared to your major product.

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