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Ethers

Ethers. Ethers are compounds with the general formula: R-O-R’ symmetrical ethers: R = R’ unsymmetrical ethers: R = R’ two lone pairs of electrons on oxygen sp 3 hybrid oxygen atom bent molecular geometry. Ethers. Ethers are commonly used as solvents in organic reactions.

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Ethers

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  1. Ethers • Ethers are compounds with the general formula: • R-O-R’ • symmetrical ethers: R = R’ • unsymmetrical ethers: R = R’ • two lone pairs of electrons on oxygen • sp3 hybrid oxygen atom • bent molecular geometry

  2. Ethers • Ethers are commonly used as solvents in organic reactions. • Polar molecules • no hydrogen bonding between ether molecules • lower BP than comparable alcohols • serves as hydrogen bond acceptor in the presence of alcohols, amines, or carboxylic acids

  3. Nomenclature of Ethers • Common Names: • Name the two alkyl groups and add the word ether • alphabetical order • in order of increasing complexity • use prefix “di” to indicate both alkyl groups are identical • if only one alkyl group is described in name, it implies the ether is symmetrical OR

  4. Nomenclature of Ethers • Examples of Common Names CH3CH2OCH3 methyl ethyl ether CH3CH2OCH2CH3 diethyl ether or ethyl ether

  5. Ethers • IUPAC Names (Alkoxy alkane) : • Ethers names as alkoxy alkanes • Use the more complex alkyl group as the base name • The other alkyl group is named as an alkoxyl group • Examples CH3CH2OCH3 methoxyethane CH3CH2OCH2CH3 ethoxyethane

  6. Ethers Example: Name the following ethers.

  7. Ethers Example: Draw the following compounds. • Methoxycyclopentane • Ethyl t-butyl ether • Chloromethyl methyl ether • (1R, 2R)-2-methoxycyclohexanol

  8. Nomenclature of Ethers • Cyclic ethers are heterocyclic compounds: • compounds containing a ring in which one or more ring atoms is an element other than carbon • Epoxide (oxirane): • three membered cyclic ether Ethylene oxide oxirane epichlorohydrin cyclohexene oxide

  9. Nomenclature of Ethers • Furan : • a five-membered aromatic cyclic ether • Tetrahydrofuran (oxolane): • saturated, five-membered cyclic ether

  10. Nomenclature of Ethers • Pyran (Oxane): • an unsaturated, six-membered cyclic ether • Dioxane: • heterocyclic ether with two oxygen atoms in a six-membered ring 1,4-dioxane

  11. Synthesis of Ethers • Williamson Ether Synthesis • SN2 attack of an alkoxide ion on an unhindered methyl or primary alkyl halide or tosylate

  12. R R R Synthesis of Ethers • Alkoxymercuration-Demercuration: • formation of Markovnikov ether from an alkene • “anti” additionto the double bond • Reagents: (1) Hg(OAc)2, ROH (2) NaBH4

  13. Synthesis of Ethers • Examples:

  14. Synthesis of Ethers • Epoxidation of Alkenes • formation of an epoxide from an alkene using a peroxyacid • Reagents: • MCPBA • CH3CO3H • Retains stereochemistry of C=C

  15. Synthesis of Ethers • Example:

  16. Synthesis of Ethers • Base-Promoted Cyclization of Halohydrins • formation of epoxides from halohydrin via internal SN2 attack of an alkoxide ion on an adjacent carbon containing a halogen • Reagents: • NaOH (aq)

  17. Synthesis of Ethers • Example:

  18. Reactions of Ethers • Autoxidation of Ethers: • spontaneous oxidation of ethers to hydroperoxides and dialkyl peroxides in the presence of atmospheric oxygen • Hydroperoxides and dialkyl peroxides are highly explosive • do not distill to dryness • use ether promptly • test old cans of ether before use

  19. Reactions of Ethers • Acid-Catalyzed Ring Opening of Epoxides • SN2 attack of water or alcohol molecule on a protonated epoxide ring • Using H+/H2O: • anti stereochemistry • Water attacks at the more substituted carbon

  20. Reactions of Ethers • Using H+/ROH: • anti stereochemistry • ROH attacks at the more substituted carbon

  21. Reactions of Ethers • Base-Catalyzed Ring Opening of Epoxides: • SN2 attack of OH- or RO- on an epoxide ring • Anti stereochemistry • OH- and RO- attack at the least hindered (least substituted) carbon in the epoxide ring

  22. Reactions of Ethers • Examples:

  23. Reactions of Ethers • Reactions of Epoxides with Grignard and Organolithium Reagents • Attack of RMgX or RLi on the least hindered carbon in the epoxide ring forming an alcohol

  24. Reactions of Ethers • Example:

  25. Ethers Examples: Predict the product of each of the following reactions.

  26. Ethers Examples:

  27. Ethers Example: How would you prepare the following compounds from the reactant given?

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