Which of the following designations accurately describes the fatty acid linoleic acid?

• A. 18:1 \( \Delta^{9} \)
• B. 20:4 \( \Delta^{5,8,11,14} \)
• C. 16:0 \( \Delta^{9} \)
• D. 18:2 \( \Delta^{9,12} \)

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the notation used to describe fatty acids. Fatty acids are typically designated by the number of carbon atoms, the number of double bonds, and the positions of the double bonds. For example, '18:2 Δ⁹,¹²' means the fatty acid has 18 carbon atoms, 2 double bonds, and the double bonds are located at the 9th and 12th carbon atoms from the carboxyl end.
2. Step 2: Recall that linoleic acid is an essential polyunsaturated fatty acid. It is characterized by having 18 carbon atoms and two double bonds, which are located at the 9th and 12th positions from the carboxyl end.
3. Step 3: Compare the given options to the correct designation of linoleic acid. The correct designation is '18:2 Δ⁹,¹²', which matches the structure of linoleic acid. The other options describe different fatty acids: '18:1 Δ⁹' refers to oleic acid, '20:4 Δ⁵,⁸,¹¹,¹⁴' refers to arachidonic acid, and '16:0 Δ⁹' is not a valid designation for a saturated fatty acid.
4. Step 4: Verify the reasoning by analyzing the structure of linoleic acid. It is a polyunsaturated fatty acid with two double bonds, and its systematic name confirms the positions of the double bonds at Δ⁹ and Δ¹².
5. Step 5: Conclude that the correct designation for linoleic acid is '18:2 Δ⁹,¹²', based on its chemical structure and the standard fatty acid nomenclature.