Cis–Trans Isomerism
By Charles Xie ✉
Cis–trans isomerism describes a phenomenon that multiple molecules have an identical chemical formula but different arrangements of atoms. A simple example of cis–trans isomerism is but-2-ene, shown as follows. The cis-2-butene has a lower melting point than the trans-2-butene, presumably because the former has a smaller contact surface to form van der Waals bonds with its kins than the latter.
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The two fatty acids, Oleic acid and elaidic acid, provide another example: Oleic acid, the cis isomer, has a melting point of 17 °C, whereas the trans isomer, elaidic acid, has the higher melting point of 44 °C. This is due to the fact that the straighter trans isomers are more likely to form more van der Waals interactions among them.
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