CH0003 - Lecture 5 - Ethers

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  1. What is an Ether?
    Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'.

    Boiling points of ethers are reduced relative to similar molecular mass alcoholic. Even though there is a molecular dipole caused by the R-OR bond, there is no hydrogen bonding
  2. What is the formula for an ether
  3. How can ethers be synthesised via acid-catalyzed condensation of alcohols? SN2
    Reagents typically H2SO4 and heat.

    In general, typically limited to symmetrical ethers of primary alcohols.

    The method is not suitable for unsymmetrical ethers.

    The substitution involves the O nucleophile of one alcohol attacking the electrophilic C in the other displacing a water molecule.

    ether synthesis by alcohol condensation
  4. What is the mechanism for ethers being synthesized via acid-catalyzed condensation of alcohols? SN2
    The mechanism of the sulfuric acid process involves the following five steps.

    1. Sulfuric acid dissociates, giving a proton plus the bisulfate ion.

    2. The alcohol's oxygen atom is protonated via an acid‐base reaction, leading to the formation of an oxonium ion.

    3. The oxonium ion decomposes, generating a 3° carbocation and water. Because carbocations are planar, this decomposition destroys the steric hindrance effect that the t‐butyl group created.

    4. In this step, the acid‐base reaction between the carbocation and a second molecule of alcohol takes place, which forms an oxonium ion.

    5. The oxonium ion liberates a proton to yield the ether.

  5. Can you make ethers from tertiary alcohols?
    Don't think so...
  6. What is an unsymetrical ether?
    An unsymmetrical ether is an ether in the molecule of which the two ligands on the ether group are different.

  7. How can you make unsymmetrical ethers?
    Don't know...
  8. How else can ethers be made, other than by acid-catalyzed condensation of alcohols?
    Ethers can also be made from the reaction of alkyl halides and the appropriate nucleophile e.g. an alkoxide

    This links to the Halo-alkane material

    Williamson Ether Synthesis
  9. What is the Williamson method of ether synthesis?
    The Williamson ether synthesis proceeds via an S N2 mechanism, in which an alkoxide ion displaces a halogen ion.

    This method cannot be used with tertiary alkyl halides, because the competing elimination reaction predominates.

    The elimination reaction occurs because the rearward approach that is needed for an S N2 mechanism is impossible due to steric hindrance.

    Williamson ether synthesis :a simple S<sub>N</sub>2 reaction
  10. What about elimination?
    Remember from halo-alkane material, strong bases will result in elimination pathways for the 3and 2o alkyl halides forming an alkene. E2
  11. What is solvolysis?
    Another way of creating ethers - from alkyl halides

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CH0003 - Lecture 5 - Ethers
2014-03-21 15:58:08
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