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Organic chemistry boiling point

  1. Jan 15, 2016 #1
    1. The problem statement, all variables and given/known data
    State true or false:
    The boiling point of propanoic acid is less than that of n-butyl alcohol, an alcohol of comparable molecular weight.

    2. Relevant equations


    3. The attempt at a solution
    Is this just a question where you either know it or don't OR is there some argument based off hydrogen bonding and the like that you can give?
     
  2. jcsd
  3. Jan 15, 2016 #2

    Borek

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    Staff: Mentor

    Try to think of one.
     
  4. Jan 15, 2016 #3
    There's hydrogen bonding in both, but because of two O atoms there is more hydrogen bonding in propanoic acid? And therefore the boiling point of propanoic acid should be more?
     
  5. Jan 15, 2016 #4

    Suraj M

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    Gold Member

    Propanoic acid is a carboxylic acid with a COOH group, so, a property of carboxylic acids in liquid state is?
    Formation of ___?
    If you get that, then you can easily answer your question.
     
  6. Jan 15, 2016 #5
    They dimerise!
    But the answer would then be true. However, if I consider greater hydrogen bonding with water, like I previously stated, the answer would be false. Which is the right explanation?
     
    Last edited: Jan 15, 2016
  7. Jan 15, 2016 #6

    Suraj M

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    Gold Member

    How did you come to that conclusion?
     
  8. Jan 15, 2016 #7

    Suraj M

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    May I know Why exactly you are bringing water into the conversation?
     
  9. Jan 15, 2016 #8
    Because if they dimerise, then between two dimers there are only van der waal interactions (because this is like intramolecular hydrogen bonding, which is why ortho nitrophenol is steam volatile). Since there are very weak interactions between different dimerised pairs, the boiling point of the liquid is less.

    Sorry, no water. Just this: There's hydrogen bonding in both, but because of two O atoms there is more hydrogen bonding in propanoic acid? And therefore the boiling point of propanoic acid should be more?
     
  10. Jan 15, 2016 #9

    Suraj M

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    Gold Member

    If you draw the diner structure you'll see that though there are hydrogen bonds within the diner the oxygen can still make more hydrogen bonds and when you say boil you'll have to separate the constituents of the dimer also, so you have to consider the interaction between them,
    Okay so I think you get the idea
    Yes propanoic acid has a higher BP
     
  11. Jan 15, 2016 #10
    OK thanks!!
     
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