Question

Which of the following classes of lipids is insoluble in ethyl ether?

• A. Triglycerides
• B. Carotenoids
• C. Sphingomyelins
• D. Cholesterol

Hint:

Phospholipids (like sphingomyelin and lecithin) contain charged phosphate groups, making them insoluble in non-polar ethers, unlike neutral fats and cholesterol.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Lipids are classified based on their structural chemistry and solubility in different organic solvents.
While simple and neutral lipids dissolve easily in highly non-polar solvents, complex polar lipids behave differently.

Step 2: Detailed Explanation:
- Triglycerides, Carotenoids, and Cholesterol: These are highly non-polar, neutral lipids. They lack charged groups and dissolve easily in non-polar organic solvents like ethyl ether and petroleum ether.
- Sphingomyelins: These are complex phospholipids containing a sphingosine backbone, a fatty acid, and a highly polar, charged phosphorylcholine head group.
- Because of this highly polar zwitterionic head group, sphingomyelins are insoluble in non-polar solvents like cold ethyl ether, but are soluble in hot alcohol or chloroform-methanol mixtures.

Step 3: Final Answer
Sphingomyelins are insoluble in ethyl ether.