In linoleic acid, where would you expect to find a double bond?

• A. 6 carbons away from the alpha end of the chain.
• B. 6 carbons away from the omega end of the chain.
• C. 3 carbons away from the omega end of the chain.
• D. On the 6 closest carbons to the omega end of the chain.
• E. 6 carbons away from the carboxylic acid group at the end of the chain.

Answer: (B)

Verified step by step guidance

1. Understand the structure of linoleic acid: Linoleic acid is a polyunsaturated fatty acid with 18 carbon atoms and two double bonds. It is classified as an omega-6 fatty acid because the first double bond is located at the sixth carbon from the omega (methyl) end of the chain.
2. Identify the alpha and omega ends of the fatty acid chain: The alpha end refers to the carboxylic acid group (-COOH), while the omega end refers to the methyl group (-CH3) at the opposite end of the chain.
3. Locate the double bonds: In linoleic acid, the first double bond is located 6 carbons away from the omega end of the chain, and the second double bond is located 9 carbons away from the omega end.
4. Clarify the terminology: The question mentions '6 carbons away from the alpha end' and '6 carbons away from the carboxylic acid group,' which are incorrect because the double bond is not counted from the alpha end but from the omega end in omega fatty acids.
5. Conclude the correct answer: Based on the structure of linoleic acid, the correct location of the first double bond is 6 carbons away from the omega end of the chain, aligning with the definition of an omega-6 fatty acid.