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14.1: Physical Properties of Ethers

  • Page ID
    183034
  • Comparisons of Physical Properties of Alcohols and Ethers

    Ether molecules have no hydrogen atom on the oxygen atom (that is, no OH group). Therefore there is no intermolecular hydrogen bonding between ether molecules, and ethers therefore have quite low boiling points for a given molar mass. Ether molecules do have an oxygen atom, however, and engage in hydrogen bonding with water molecules. Consequently, an ether has about the same solubility in water as the alcohol that is isomeric with it. For example, dimethyl ether and ethanol (both having the molecular formula C2H6O) are completely soluble in water, whereas diethyl ether and 1-butanol (both C4H10O) are barely soluble in water (8 g/100 mL of water).  Indeed, ethers have boiling points about the same as those of alkanes of comparable molar mass and much lower than those of the corresponding alcohols as shown in the table below.

    Table. Comparison of Boiling Points of Alkanes, Alcohols, and Ethers
    Condensed Structural Formula Name Molar Mass Boiling Point (°C) Intermolecular Hydrogen Bonding in Pure Liquid?
    CH3CH2CH3 propane 44 –42 no
    CH3OCH3 dime thyl ether 46 –25 no
    CH3CH2OH ethyl alcohol 46 78 yes
    CH3CH2CH2CH2CH3 pentane 72 36 no
    CH3CH2OCH2CH3 diethyl ether 74 35 no
    CH3CH2CH2CH2OH butyl alcohol 74 117 yes

    Ethers are Good Solvents for Many Organic Reactions

    Ethers can only accept H-bonds, while alcohols are both H-bond donors and acceptors.  The ability of ethers to accept H-bonds combined with the London forces of the alkyl groups bonded to the oxygen allows ethers to be excellent solvents for a wide range of organic compounds.  The low chemical reactivity of ethers also makes ethers a preferred solvent for many organic reactions.  Additionally, the high volatility of ethers allows for their evaporation when isolating reaction products.

    ether solvation.jpg

    Exercise

    1. Draw the bond-line structures and arrange the following ethers in order of increasing boiling point: 1-propoxybutane, diethyl ether, 1-ethoxybutane, dibutyl ether.

    2. Arrange the following ethers in order of increasing water solubility: 1-propoxybutane, diethyl ether, 1-ethoxybutane, dibutyl ether.

    Answer
    1.

      ch 16 sect 1 exercise 1 solution.png

    2.

     

    ch 16 sect 1 exercise 2 solution.png

     

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