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Which has the highest boiling point?

  1. Apr 18, 2016 #1
    1. The problem statement, all variables and given/known data
    Which one of these had the highest boiling point?
    A. 3-Pentanone B. 1-Butanol C. Butanal

    2. Relevant equations


    3. The attempt at a solution
    The answer should be 3-pentanone because
    1- it's molecular weight is approx 76 compared to the other which has approx 64
    2 - because of the dipole-dipole attraction.

    However when I googled the boiling points for each one it says that Butanol has the highest. Why is it that?
     
  2. jcsd
  3. Apr 18, 2016 #2

    Borek

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    Staff: Mentor

    What kinds of intermolecular bonds/interactions/forces do you know?
     
  4. Apr 18, 2016 #3
    I know the dipol-dipol attraction which is between carbon and oxygen and the Hydrogen bond which is as a result of unshared pare of electrons and the hydrogen.
     
  5. Apr 18, 2016 #4

    Borek

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    Staff: Mentor

    Which is stronger? And which apply to which of these molecules?
     
  6. Apr 18, 2016 #5
    Hydrogen bond is stronger and it applies to alcohols.
    So, does that mean that alcohols always have higher boiling points than ketones/aldehydes regardless of their molecular weight?

    However, if an alcohol has branching and the ketone does not, then the alcohol will have lower boiling points am I correct?
     
  7. Apr 18, 2016 #6

    Borek

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    Staff: Mentor

    Not necessarily.

    Actually this is quite tricky, as such simplified comparisons work best with the assumption "all other things kept constant".

    In this particular case all three molecules are reasonably similar when it comes to the molecular mass, so the answer is more or less obvious, hydrogen bonding should make the difference. But when the mass difference becomes larger things become less obvious.
     
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