Question

Which compound has a lower melting point, explain the chemical basis of choice.

a. palmitic (a saturated fatty acid)

or

b. palmitoleic acid (a cis-monounsaturated fatty acid)

Answer 1

Melting points of unsaturated fatty acids are much lower than those of saturated fatty acids
with the same number of carbon atoms. that means b.palmitoleic acid has lower melting point.

The m.p. of unsaturated fatty acids are much lower because the cis configuration
produces a bend/kink in the structure which decreases the number of possible van der Waals
interactions between molecules and same kink/bend which makes it more difficult to pack their molecules together in a stable repeating array or crystalline lattice.

The higher melting points of the saturated fatty acids --- the uniform rod-like shape of their molecules make it close intermolecular interactions result in relatively high melting points