Part B Epoxides

Cyclic ethers are normally quite stable. For example, THF (tetiahydrofliran) is commonly used as a solvent because it provides a polar medium for carrying out polar reactions without itself reacting. 

In contrast, a three-member cyclic ether (e.g., epoxide) is highly strained and reactive. Such rings are commonly used in synthesis, beeause, like bromonium ion rings, they lead to stereoselective products. 

Though the result above is most important, a mechanism is provided below in case it helps you remember the reaction. R R 

Model 5 Acid-Catalyzed Epoxide Ring Opening (Acidic Conditions) 

Reaction with an acid is often called protonation because the fimction of the acid is to transfer an Ift, and an H atom with no electrons (tf) is simply a proton. 

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