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Alcohols and ethers

Alcohols and ethers. Structure. R-OH alcohol R = alkyl group (substituted or unsubstituted). Sterols - the steroid ring system. Physical properties of alcohols.

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Alcohols and ethers

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  1. Alcohols and ethers

  2. Structure R-OH alcohol R = alkyl group (substituted or unsubstituted)

  3. Sterols - the steroid ring system

  4. Physical properties of alcohols Alcohols are noticeably less volatile; their melting points are greater and they are more water soluble than the corresponding hydrocarbons having similar molecular weights. These differences are due to the OH group which renders a certain polarity to the molecule. The result is an important intermolecular attraction:

  5. Solubility of alcohols Low molecular weight alcohols are water soluble:

  6. Spectroscopic properties IR: Unassociated alcohols show a fairly sharp absorption near 3600 cm-1 due to O-H stretching. Associated alcohols (hydrogen bonded) show a broad absorption in the 3300 - 3400 cm-1 range.

  7. Fermentation Fermentation of sugar by yeast gives C2H5OH. Methanol is added to denature it.

  8. Azeotropic mixtures The bp of ethanol is 78.3C whereas that of water is 100C (at least on Vancouver’s waterfront!). Can we separate a mixture by distillation? No! An azeotropic mixture forms! An azeotropic mixture is one whose liquid and vapor forms have identical compositions. The mixture cannot be separated by distillation. eg C2H5OH (95%) and H2O (5%) - bp 78.13C H2O (7.5%), C2H5OH (18.5%) and C6H6 (74%) - bp 64.9C

  9. Oxymercuration

  10. Hydroboration syn addition

  11. Reactions of alcohols The reactions of alcohols involve one of two processes: • breaking of the O-H bond • breaking of the C-O bond

  12. Reactions involving O-H bond breaking R-OH + M RO- + M+ + 1/2 H2

  13. Reactions involving C-O bond breaking - dehydration

  14. Reactions involving C-O bond breaking - dehydration E1 mechanism

  15. Reaction with hydrogen halides

  16. Experimental facts 1. The reaction is acid catalyzed 2. Rearrangements are possible 3. Alcohol reactivity is 3o > 2o > 1o < CH3OH

  17. The mechanism

  18. Reaction of primary alcohols with HX SN2 This reflects nucleophile strength in a protic solvent.

  19. Reactions with phosphorus halides and with thionyl chloride ROH + PX3 RX + H3PO3 Creates a good leaving group from 1o and 2o alcohols.

  20. Tosylates

  21. Why form tosylates? Sulfonate ions are excellent leaving groups:

  22. Ethers Structure: R-O-R, Ar-O-R, or Ar-O-Ar nomenclature Name the two groups bonded to the oxygen and add the word ether. CH3CH2OCH2CH3 - diethyl ether

  23. Nomenclature of ethers diphenyl ether methyl vinyl ether CH3OCH=CH2 isopropyl phenyl ether 3-methoxyhexane CH3CH2CH2CHCH2CH3 | OCH3

  24. Nomenclature of cyclic ethers Use the prefix oxa- to indicate that an O replaces a CH2 in the ring. oxacyclopropane ethylene oxide oxacyclopentane tetrahydrofuran 1,4-dioxacyclohexane 1,4-dioxane

  25. Williamson synthesis A primary halide is necessary to ensure an SN2 reaction and not an E2 elimination.

  26. Reaction of ethers What is the mechanism?

  27. Reaction of ethers 1-Ethoxybutane reacts with HI to give a mixture of 1-iodobutane, iodoéthane, ethanol and1-butanol whereas 2-ethoxy-2-methylpropane gives a mixture of 2-methyl-2-propanol and iodoethane. Explain.

  28. Epoxides syn addition

  29. Mechanism

  30. Reactions What is the mechanism?

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