Chapter 18 October 3 - Reaction of epoxides with HX...

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1 Reactions of Ether: 2. Claisen Rearrangement General Structure: Initial Ether Formation: Claisen Rearrangement: Specific to allyl aryl ethers Pericyclic Reaction (concerted)
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2 Mechanism: Example:
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3 Epoxides: A Type of Cyclic Ether Epoxide Preparation: 3­Membered ring cyclicethers known as oxiranes The ring strain (angle strain specifically) gives epoxides their reactivity
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4 Mechanism (alkene + peroxy acid): Synthesis Involving Halohydrins: Mechanism:
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5 Epoxide Reactions: Acid Catalyzed Ring Opening Example: Mechanism: Epoxides can be cleaved in acidic conditions just like ethers (hydrolysis) They react under much milder conditions due to ring strain
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6 Formation of Halohydrins Via an Epoxide Ring Opening: Example: What happens if the epoxide isn't symmetrical?
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Unformatted text preview: Reaction of epoxides with HX produces halohydrins (X = Br, Cl, I, or F) If both carbons in the epoxide are 1 o /2 o , the Nu attacks the less hindered site (S N 2 like) If one of the carbons is 3 o , the Nu attacks the most highly substituted site (S N 1 like) 7 Stereochemistry?? Mechanism?? 8 Base Catalyzed Epoxide Ring Openings: Hydroxide: Grignard: Example: Example: . Base catalyzed epoxide ring opening is a typical S N 2 reaction nucleophile attacks the least hindered carbon 9 Crown Ethers: Naming Example: Large rings consisting of repeating (OCH 2 CH 2 ) Units X = total number of ring atoms Y = number of oxygens...
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This note was uploaded on 12/20/2011 for the course CHEM 234-54 taught by Professor Morrison during the Fall '09 term at University of Georgia Athens.

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Chapter 18 October 3 - Reaction of epoxides with HX...

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