Advanced Topic 870 of 1102 Organic Chemistry
Epoxides
Strained three-membered cyclic ethers that open readily with nucleophiles.
In-depth explanation of Epoxides
Epoxides are three-membered cyclic ethers in which the oxygen is part of a strained ring, with a ring strain of about 115 kJ/mol. Their strain makes them much more reactive than open-chain ethers, so they readily undergo ring-opening by nucleophiles. Under basic or neutral conditions the nucleophile attacks the less hindered carbon by an SN2 pathway. Under acidic conditions the epoxide is first protonated, and the nucleophile attacks the more substituted carbon, which carries more positive character. Epoxides are made by treating alkenes with peracids.
Going deeper: Epoxides
Key ideas: Three-membered cyclic ethers with strain energy of about 115 kJ/mol, made by peracid (mCPBA) epoxidation of alkenes (syn, stereospecific) or from halohydrins with base. Ring opening: under basic or nucleophilic conditions (SN2) the nucleophile attacks the less hindered carbon; under acidic conditions it attacks the more substituted carbon, with inversion at that carbon, giving trans products. Ethylene oxide with water gives ethylene glycol.
Common mistakes and connections: Students predict the wrong regiochemistry by mixing acid and base conditions. Another error is forgetting that ring opening needs no leaving group other than the strain relief. Grignard reagents add to epoxide giving alcohols with two more carbons. Links to ring strain, Sharpless epoxidation, SN2 and antifreeze production.
Visualization of Epoxides
Three-membered cyclic ethers carry about 114 kJ/mol of ring strain, which is why they open readily with nucleophiles. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Ethylene oxide reacts with water to give ethylene glycol, a diol used as antifreeze.
Frequently asked questions about Epoxides
What is Epoxides?
Strained three-membered cyclic ethers that open readily with nucleophiles.
Is Epoxides a beginner, intermediate or advanced topic?
Epoxides is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Epoxides?
Study these earlier topics in Organic Chemistry first: Baeyer's Reagent, Williamson vs Elimination, Reduction of Carbonyls.
What comes after Epoxides?
The next topics in Organic Chemistry are Sharpless Epoxidation and Hydroboration-Oxidation.
Can I practise Epoxides with quizzes?
Yes. The interactive lesson includes a self-check question on Epoxides, and the Organic Chemistry quiz draws on every topic in this area.
Where Epoxides fits in Organic Chemistry
Epoxides is topic 142 of 148 in Organic Chemistry.