Resonance and Boiling Point - Question Regarding Chad's Quizzes

[spdental]

One of Chad's Quizzes has a multiple choice question asking which one of the following statements is correct, and one of his answers (not the correct one) is: "Resonance decreases the boiling point of compounds."

In the video answer he says that resonance doesn't have a direct effect on the boiling point, but if boiling point increases with increasing intermolecular forces, and resonance decreases intermolecular forces, then wouldn't you be correct in saying that an isomer with resonance should have a lower boiling point than another without resonance?

Thanks!

---

Members don't see this ad.

 

[deleted738762]

One of Chad's Quizzes asks which one of the follow statements is correct, and one of his answers (not the correct one) is: "Resonance decreases the boiling point of compounds."

In the video answer he says that resonance doesn't have a direct effect on the boiling point, but if boiling point increases with increasing intermolecular forces, and resonance decreases intermolecular forces, then wouldn't you be correct in saying that an isomer with resonance should have a lower boiling point than another without resonance?

Thanks!

I never learned that resonance decreases IMF. I learned resonance and boiling point have no correlation, so resonance then has no correlation with IMF. If there was a question like that, it probably won't show up on the DAT.

 

[spdental]

I never learned that resonance decreases IMF. I learned resonance and boiling point have no correlation, so resonance then has no correlation with IMF. If there was a question like that, it probably won't show up on the DAT.

Resonance spreads out the charge among different atoms, therefore decreasing the electronegativity, which I would assume would correlate to a decreasing innermolecular force. I'm sure it won't be on the DAT, I'm just curious.

 

[deleted738762]

Resonance spreads out the charge among different atoms, therefore decreasing the electronegativity, which I would assume would correlate to a decreasing innermolecular force. I'm sure it won't be on the DAT, I'm just curious.

I agree with you it makes sense.

 

[DAT Destroyer]

One of Chad's Quizzes has a multiple choice question asking which one of the following statements is correct, and one of his answers (not the correct one) is: "Resonance decreases the boiling point of compounds."

In the video answer he says that resonance doesn't have a direct effect on the boiling point, but if boiling point increases with increasing intermolecular forces, and resonance decreases intermolecular forces, then wouldn't you be correct in saying that an isomer with resonance should have a lower boiling point than another without resonance?

Thanks!

This is what I call a " loaded " question and a poor one at that. It would depend on many factors. As a good general rule, boiling and melting point is governed by intermolecular factors. However, I will answer your question. Let us take the amide as an example. This family has ENORMOUS melting and boiling points because of the huge contribution of the ionic resonance hybrid !!!!! Thus, clearly you see resonance could indeed explain this trend. Amides can reach over 250C !!! If you have a hydrocarbon that is water insoluble with a low boiling point one would not bat any eye, but some hydrocarbons that are aromatic have resonance forms that are charged, hence would present with higher than predicted physical properties such as solubility, dipole, and boiling point ! However, resonance normally does not have such a large role when it comes to properties such as boiling points or melting points. If a resonance form that is a major contributor dominates over a charged contributor as seen in ketones, we would predict a lower boiling point than possibly anticipated. Thus, as you can see, this question can have an answer that can go many ways !!!!

I hope this helps.

Dr. Romano