Q. 15.25 - An Introduction to General, Organic, and Biological Chemistry

Question

Safflower oil is polyunsaturated, whereas olive oil is monounsaturated. Why would safflower oil have a lower melting point than olive oil?

Step-by-Step Solution

Answer

Due to the presence of fatty acids with two or three double bonds in its structure, safflower oil has a lower melting point than olive oil; nevertheless, olive oil's structure contains an indicated amount of oleic acid, which is known to have a single double bond (monounsaturated).

Step 1: Introduction

• Lipids are hydrophobic esters of intermediate to long-chain fatty acids.
• Saturated and unsaturated fatty acids are the two forms of fatty acids.
• Unsaturated fatty acids have a long chain of carboxylic acids with double or triple bonds in their structure. 
• The fatty acid chain is said to be saturated when it contains all of the single bonds in its structure. 

Step 2: Explanation for Saturated and Unsaturated fats

• The fatty acid chains in saturated fats form a regular pattern, with many dispersive forces acting in between them. 
• So, even though they are weak intermolecular forces, they produce a strong bond when they are near together. 
• As a result, high temperatures are required to shatter them.
• The bend generated by the double bond disrupts the symmetry of unsaturated fats and weakens the dispersion of forces between the carbon chains. 
• As a result, the chains are only loosely bound together, causing them to melt at lower temperatures.

Step 3: Determine the safflower oil have a lower melting point than olive oil

• A rigorous ${30}^{\circ }$bend in the structure of fatty acids is ensured by the presence of a "cis" double bond.
• The melting point is lower as a result.
• The melting point of safflower oil is lower than that of olive oil because both are polyunsaturated.