Anti Addition vs Syn Addition - Alkene Reactions | Summary and Q&A

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April 4, 2023
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Anti Addition vs Syn Addition - Alkene Reactions

TL;DR

Different reagents result in either anti-addition or syn-addition when reacting with one methyl cyclohexene.

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Questions & Answers

Q: What is the result of reacting one methyl cyclohexene with hydrogen gas using a platinum catalyst?

The reaction proceeds with sin-addition, adding two hydrogens on the same side across the double bond. This is known as syn-addition.

Q: How does potassium permanganate under basic conditions react with one methyl cyclohexene?

Potassium permanganate under basic conditions results in dihydroxylation with syn-addition. It adds hydroxyl groups to both carbons of the double bond.

Q: What are the steps and outcomes of hydroboration with BH3 THF followed by oxidation with hydrogen peroxide and hydroxide?

The hydroboration step adds a hydrogen and an OH group, with sin-addition. The OH group goes on the less substituted carbon, and the hydrogen goes on the more substituted carbon. The oxidation step converts the boron intermediate to an alcohol without changing the addition pattern.

Q: How does reacting one methyl cyclohexene with Br2 and methanol proceed?

The reaction proceeds with anti-addition. A bromine atom is added to the less substituted secondary carbon, while an OCH2 group is added to the more substituted tertiary carbon.

Summary & Key Takeaways

  • Hydrogen gas with a platinum catalyst results in sin-addition, adding two hydrogens on the same side across the double bond.

  • Potassium permanganate under basic conditions leads to dihydroxylation with syn-addition, producing a diol.

  • Hydroboration with BH3 THF followed by oxidation with hydrogen peroxide and hydroxide results in sin-addition, adding an OH group to the less substituted carbon and a hydrogen to the more substituted carbon.

  • Br2 with methanol proceeds with anti-addition, adding a bromine atom to the less substituted carbon and an OCH2 group to the more substituted carbon.

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