Multiple Choice
Which of the following fatty acids would you expect to be more soluble in cyclohexane?
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23. Lipids
Fatty Acids
4:38 minutesProblem 5
Textbook Question
Draw the complete structural formula of arachidonic acid (Table 23.1) in a way that shows the cis stereochemistry of its four double bonds.
Verified step by step guidance1
Identify the molecular structure of arachidonic acid: Arachidonic acid is a polyunsaturated fatty acid with the molecular formula C20H32O2. It contains 20 carbon atoms, 4 cis double bonds, and a carboxylic acid functional group (-COOH) at one end.
Determine the positions of the double bonds: The four double bonds in arachidonic acid are located at carbons 5-6, 8-9, 11-12, and 14-15. All of these double bonds have cis (Z) stereochemistry, meaning the hydrogen atoms attached to the double-bonded carbons are on the same side.
Draw the carbon chain: Start by drawing a straight chain of 20 carbon atoms. Label the carbons from 1 to 20, with carbon 1 being part of the carboxylic acid group (-COOH) and carbon 20 being the terminal methyl group (-CH3).
Add the double bonds with cis stereochemistry: For each double bond (5-6, 8-9, 11-12, and 14-15), draw the bond as a double line (=) and ensure the hydrogens on the double-bonded carbons are on the same side of the chain. This represents the cis configuration.
Complete the structure: Add single bonds (-) between all other carbons and attach the appropriate number of hydrogens to each carbon to satisfy the octet rule. Ensure the carboxylic acid group (-COOH) is fully drawn at carbon 1, and the terminal methyl group (-CH3) is at carbon 20.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Arachidonic Acid Structure
Arachidonic acid is a polyunsaturated fatty acid with a 20-carbon chain and four double bonds. Its structural formula includes a long hydrocarbon tail with specific locations of double bonds, which are crucial for its biological function. Understanding its structure is essential for recognizing how it interacts with enzymes and receptors in the body.
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Cis Stereochemistry
Cis stereochemistry refers to the arrangement of substituents around a double bond where the substituents are on the same side. In the context of arachidonic acid, the cis configuration of its double bonds affects the molecule's shape and reactivity, influencing its role in biological processes such as inflammation and cell signaling.
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Structural Formula Representation
A structural formula visually represents the arrangement of atoms within a molecule, including bonds and stereochemistry. For arachidonic acid, accurately depicting its structural formula involves showing the carbon backbone, double bonds, and the cis configuration, which is vital for understanding its chemical properties and biological functions.
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