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Which has the highest boiling point?

  • Thread starter Sall1230
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  • #1
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Homework Statement


Which one of these had the highest boiling point?
A. 3-Pentanone B. 1-Butanol C. Butanal

Homework Equations




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?
 

Answers and Replies

  • #2
Borek
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What kinds of intermolecular bonds/interactions/forces do you know?
 
  • #3
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What kinds of intermolecular bonds/interactions/forces do you know?
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.
 
  • #4
Borek
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Which is stronger? And which apply to which of these molecules?
 
  • #5
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Which is stronger? And which apply to which of these molecules?
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?
 
  • #6
Borek
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does that mean that alcohols always have higher boiling points than ketones/aldehydes regardless of their molecular weight?
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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