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I've learnt that cis isomers have higher boiling point than the trans ones. Why does not that rule apply on Fumaric and maleic acids?

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In the case of fumaric acid, intermolecular hydrogen bonds are the reason beyond its higher melting point compared with the melting point of maleic acid ( where intramolecular hydrogen bonds dominate).

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  • $\begingroup$ can you tell me more about this. $\endgroup$ – user2390934 Apr 13 '16 at 9:59
  • $\begingroup$ In the case of fumaric acid, the molecules are linked to each other via hydrogen bonds. To melt the fumaric acid, one has to provide additional energy to break up hydrogen bonds before the solid turns into liquid. I hope it's clear now. $\endgroup$ – Yomen Atassi Apr 13 '16 at 16:19

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