Why do trans fatty acids have higher melting points than cis fatty acids?

Trans fatty acids have higher melting points than cis fatty acids because of their molecular shape and packing efficiency.

In a cis configuration, the carbon chain is bent at the double bond, which prevents the molecules from packing closely together in a regular, parallel arrangement. Because these molecules remain farther apart, less energy is required to separate them, resulting in a lower melting point.1

In contrast, the trans configuration allows the hydrocarbon chain to remain in a more extended, linear shape, similar to that of a saturated fatty acid. This structure enables the molecules to stack and pack together more tightly and efficiently in a crystalline lattice. Because these molecules can pack more closely, more energy is required to overcome the intermolecular forces and melt the substance, leading to a higher melting point.21