Which has the highest boiling point?

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Discussion Overview

The discussion revolves around the boiling points of three organic compounds: 3-Pentanone, 1-Butanol, and Butanal. Participants explore the factors influencing boiling points, particularly focusing on molecular weight and intermolecular forces such as hydrogen bonding and dipole-dipole interactions.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that 3-Pentanone should have the highest boiling point due to its molecular weight and dipole-dipole attractions.
  • Another participant notes that online sources indicate 1-Butanol has the highest boiling point, prompting questions about the reasons behind this discrepancy.
  • Participants discuss various intermolecular forces, including dipole-dipole interactions and hydrogen bonding, with one participant asserting that hydrogen bonds are stronger and apply to alcohols.
  • There is a query about whether alcohols always have higher boiling points than ketones and aldehydes, regardless of molecular weight, which is met with skepticism.
  • One participant points out that simplified comparisons of boiling points depend on the assumption that all other factors are constant, indicating that variations in molecular structure can complicate these comparisons.

Areas of Agreement / Disagreement

Participants express differing views on the boiling points of the compounds in question, with no consensus reached regarding the influence of molecular weight versus intermolecular forces. The discussion remains unresolved as participants explore the complexities involved.

Contextual Notes

Participants acknowledge that comparisons of boiling points may vary based on molecular structure and the presence of branching, indicating that assumptions about constant conditions may not hold true in all cases.

Sall1230
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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?
 
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What kinds of intermolecular bonds/interactions/forces do you know?
 
Borek said:
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.
 
Which is stronger? And which apply to which of these molecules?
 
Borek said:
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?
 
Sall1230 said:
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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