alkene melting point

[toothfairy05]

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I don't get why a trans alkene has a higher melting point than a cis alkene. Kaplan explains that it's because of symmetry. It just seems counterintuitive to me since symmetric molecules can pack closer together-- shouldn't this lower the melting point?

Thanks!

 

[whatDATmean]

Packing allows it to stick together better or be in the solid form more than the liquid form. Since packing make it a better solid its less likely to become a liquid or "melt".

That's how I think of it. 😀

 

[ScratchMan]

Due to dipole-dipole moment. Cis alkene could have better dd than trans alkene. Think about dichloroethene for cis & trans.

 

[2PacClone23]

I thought the more stable compound always had the higher MP and BP.


Wouldn't that be cis?

 

[healthcaree]

I thought the more stable compound always had the higher MP and BP.


Wouldn't that be cis?

more stable would be trans.

 

[toothfairy05]

I just read that the melting points also has to do with polarity. The trans-alkene is less polar, this gives it a higher melting point. As a result, the cis-alkene which is more polar, has a lower melting point and consequently, a higher boiling point.

Thanks everyone, just discussing it made this concept more clear for me 🙂