Chapter 11.9: Reactions of Epoxides

Question 1

What is the stereochemistry of acid-catalyzed epoxide ring opening?

Answer 1

anti

Question 2

What is the stereochemistry of nucleophilic epoxide ring opening?

Answer 2

Anti

Question 3

Describe the mechanism behind the nucleophilic opening of an epoxide ring

Answer 3

 Step 1: Make a new bond between a nucleophile and an electrophile and simultaneously break a bond to give stable molecules or ions
• Backside attack of the nucleophile on the less hindered carbon of the highly strained epoxide opens the ring and displaces O-
 Step 2: Add a proton
• Proton transfer completes the reaction

Question 4

What is the regiochemistry of acid-catalyzed epoxide ring opening?

Answer 4

Markovnikov

Question 5

What is the regiochemistry of nucleophilic epoxide ring opening?

Answer 5

less hindered carbon

Question 6

Describe the mechanism behind acid-catalyzed hydrolysis of an epoxide

Answer 6

 Step 1: Add a Proton
• Proton transfer from the acid catalyst to oxygen of the epoxide gives a bridged oxonium ion intermediate
 Step 2: Make a New Bond Between a Nucleophile and an Electrophile and Simultaneously Break a Bond to Give Stable Molecules or Ions
• Backside attack of H2O on the protonated epoxide opens the three-membered ring
 Step 3: Take a proton away
• Proton transfer to solvent completes the formation of the glycol