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What stereoisomers are obtained from hydroboration–oxidation of cis -2-butene?

Answer 1

Brooklyn Barber

The product is a racemic mixture of (#R#)-butan-2-ol and (#S#)-butan-2-ol.

If the BH₃ attacks from the top of the alkene

we get the borane

The product on oxidation with H₂O₂ is (#S#)-butan-2-ol.

If the BH₃ attacks from the bottom of the alkene

we get the borane

The product on oxidation with H₂O₂ is (#R#)-butan-2-ol.

There is an equal chance of attack from top or bottom, so we get a 50:50 mixture of the two stereoisomers.

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Answer 2

Ruby Allen

The stereoisomers obtained from hydroboration–oxidation of cis-2-butene are the same. Hydroboration–oxidation of cis-2-butene yields a single product, which is (2R,3S)-butan-2-ol.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.