Ochem-Ch18-Ethers

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Author:
lukemlj
ID:
73624
Filename:
Ochem-Ch18-Ethers
Updated:
2011-03-20 05:47:34
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Ochem Ethers
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Description:
Ochem CH18 Ethers, Epoxides, Thiols, Sulfides
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  1. CH3CH2-OH ---(H+)--->
    • CH3CH2-O(+)H2 --- CH3CH2-OH ---->
    • CH3CH2-O-CH3CH2 + H(+)
  2. Ether Synthesis: Williamson
    • R-OH + NaH ---> RO(-)Na(+) + H2
    • , where X: Cl, Br, I, OTos
  3. What carbon should the leaving group be on in a Williamson reaction?
    The least substituted carbon
  4. Ether Synthesis: Alkoxymercuration
  5. What is a limitation of alkoxymercuration in ether synthesis?
    Ditertiary ethers cannot be formed due to steric hindrance.
  6. Ether Reactions: Cleavage
  7. What acids can be used to cleave ethers?
    HBr and HI. NOT HCl
  8. An ether with only primary and secondary alkyl groups undergo cleavage by what type of substitution and on which alkyl group?
    • Sn2
    • Less hindered
  9. An ether with a tertiary, benzyllic, or allylic alkyl group usually undergoes cleavage by what mechanism?
    Sn1
  10. Ether Reactions: Claisen
  11. Claisen rearrangement is specific to what type of ether?
    Allyl aryl
  12. mCPBA
    
  13. MMPP
  14. In acid-induced opening of expoxides with HBr, there is a high degree of Sn___ character which leads to OH being formed on the more stable ___, i.e. ___.
    1, cation, tertiary
    • Can use OH or CH3MgBr instead of RO-
  15. What is the importance of Crown ethers?
    • They solvate metal cations such as K+
    • Enhances Sn2 reactivity of an anion
  16. What is a mercaptan?
    A Thiol
  17. What is the most striking characterestic of a thiol?
    The horrible odor - skunk, onion, garlic, additive for natural gas.
  18. Thiols are like alcohols, but are ____ bases and ____ nucleophiles.
    stronger, better
  19. A sulfide is like an analog of what?
    An ether. Sulfide: R-S-R
  20. Thiol Synthesis
  21. Thiol Synthesis
    • ---OH(-)--->
  22. Oxidation of Thiols
  23. R-SH ----NaH--->
    RS(-)
  24. Unlike dialkyl ethers, dialkly sulfides are ___ nucleophiles that react with primary alkyl halides by an ___ mechanism to give ____.
    good, Sn2, sulfonium ions S+(R)3
  25. Oxidation of Sulfides
    • If R=R'=CH3, product is DMSO
  26. Oxidation of Sulfides
  27. What is anisole?
  28. What makes ethers good solvents?
    • Polar
    • Aprotic
    • Relatively inert
    • Cheap
  29. What are the cons of ethers as a solvent?
    Flammable/explosive
  30. Ethers are prepared by either ___ which involves ___ reaction of an alkoxide with a primary alkyl halide, or the ___ reaction which involves Markovnikov addition of an alcohol to an alkene.
    Williamsom ether synthesis, Sn2, alkoxymercuration
  31. Ethers are inert to most reagents but react with ___ to give cleavage products.
    strong acids
  32. Cleavage of ethers takes place by an ___ mechanism at the ___ highly substituted site if only ___ alkyl groups are bonded to the either oxygen, but by an ___ mechanism if one of the alkyl groups is ___.
    Sn2, less, primary and secondary, Sn1 or E1, tertiary
  33. ___ ethers undergo Claisen rearrangement to give ___.
    Aryl allyl, o-allylphenols.
  34. Due to ___, epoxides undergo a ___ reaction with both acids and bases.
    strain, cleavage
  35. In epoxides, acid cleavage of the C-O bond at the ___ highly substituted site occurs if both epoxide carbons are ___, but occurs at the ___ highly substituted site if one of the epoxide carbons is ___.
    less, primary or secondar, more, tertiary
  36. Base-catalyzed epoxide ring-opening occurs by ___ reacition of a ___ at the ___ hindered epoxide carbon.
    Sn2, nucleophile, less
  37. Thiols, the sulfur analogs of ___, are usually prepared by ___ reaction of ___ with thiourea.
    alcohols, Sn2, an alkyl halide
  38. Mild oxidation of a thiol yields a ___, and mild reduction of a ___ gives back the thiol.
    disulfide, disulfide
  39. Sulfides are prepared by an ___ reaction between a ___ and a ___.
    Sn2, thiolate anion, primary or secondary alkyl halide
  40. Sulfides are much more ___ than ethers and can be oxidized to ___ and ___.
    nucleophilic, sulfoxide, sulfones
  41. Sulfides can be alkylated by reaction with ___ to yield ___.
    a primary alkyl halide, sulfonium ions.

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