Question

Why do unsaturated fatty acids have lower melting points than saturated fatty acids?

Answer 1

The carbon = carbon double bonds in unsaturated fatty acids are restricting the movement of the molecule branches. They are more "kinked" up and do not pack as tightly. whereas, saturated fatty acids have more freedom of movement and tend to pack together better. Therefore, in the case of unsaturated fatty acids they can not compact tightly together and there are less van der Waals interactions between the molecules, and so the melting point is reduced.