Which statement correctly describes how the degree of unsaturation in fatty acids influences melting point?

Which statement correctly describes how the degree of unsaturation in fatty acids influences melting point?

• A. Saturated fatty acids have no double bonds and pack tightly, giving higher melting points.
• B. Monounsaturated fatty acids have more than one double bond, which increases packing and raises melting point.
• C. Polyunsaturated fatty acids have no double bonds and melt at higher temperatures.
• D. The degree of unsaturation does not affect melting point.

Answer: (A)

The main idea here is how the shape and packing of fatty acid chains affect melting point. Saturated fatty acids have no double bonds, so their chains are straight and can pack very tightly in a solid arrangement. That tight packing increases the strength of intermolecular van der Waals interactions, meaning more heat is needed to break the lattice and melt the substance. So, saturated fats generally have higher melting points because their straight chains allow close, stable packing. Introducing double bonds bends the chains. Those kinks disrupt tight packing, reduce intermolecular contacts, and lower the energy required to melt the material. As unsaturation increases, the melting point tends to decrease. That’s why the statement describing saturated fatty acids as having no double bonds and packing tightly with higher melting points is the best description. The other ideas don’t fit: adding multiple double bonds doesn’t raise packing and melting point, polyunsaturated fats aren’t free of double bonds, and the degree of unsaturation does influence melting point.

The main idea here is how the shape and packing of fatty acid chains affect melting point. Saturated fatty acids have no double bonds, so their chains are straight and can pack very tightly in a solid arrangement. That tight packing increases the strength of intermolecular van der Waals interactions, meaning more heat is needed to break the lattice and melt the substance. So, saturated fats generally have higher melting points because their straight chains allow close, stable packing.

Introducing double bonds bends the chains. Those kinks disrupt tight packing, reduce intermolecular contacts, and lower the energy required to melt the material. As unsaturation increases, the melting point tends to decrease. That’s why the statement describing saturated fatty acids as having no double bonds and packing tightly with higher melting points is the best description.

The other ideas don’t fit: adding multiple double bonds doesn’t raise packing and melting point, polyunsaturated fats aren’t free of double bonds, and the degree of unsaturation does influence melting point.