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Topic: Why does fluorenone have a lower melting point than fluorene?  (Read 1660 times)

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Offline oakthomas

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Why does fluorenone have a lower melting point than fluorene?
« on: January 31, 2021, 06:46:35 PM »
More polar molecules have higher melting points. So why is polar fluorenone's lower than non-polar fluorene?
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Offline Borek

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Re: Why does fluorenone have a lower melting point than fluorene?
« Reply #1 on: February 01, 2021, 03:08:38 AM »
It is just a rule of thumb and as such almost never exact. A lot depends on the molecule shape, size and steric effects. My guess would be fluorene molecules are getting packed much more closer to each other in the crystal structure, so their interactions are much stronger - but that's just intuition.
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Offline AWK

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Re: Why does fluorenone have a lower melting point than fluorene?
« Reply #2 on: February 02, 2021, 01:29:41 AM »
As Borek emphasized, polarity is not the only property that determines the melting point of solids, especially more complex molecules. There are two polymorphs of fluorenone with melting points of 72.8°C and 84.4°C. How do you explain it just by polarity?
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