23. Lipids

Which of the following fatty acids would you expect to be more soluble in cyclohexane?

Provide a condensed structural formula for a fatty acid with 18 carbons (18:0) and give its common name.

Provide a skeletal structure for Linolenic acid.

Use Figure 23.1 to identify the family of lipids to which each of these molecules belongs.

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Draw the complete structural formula of arachidonic acid (Table 23.1) in a way that shows the cis stereochemistry of its four double bonds.

Draw an 18-carbon saturated fatty acid. Is this a “straight-chain” molecule or a “bent” molecule?

Draw an 18-carbon unsaturated fatty acid that contains two carbon–carbon double bonds, one on carbon 6 and one on carbon 9 (count starting with the carboxyl carbon). Is this a “straight-chain” molecule or a “bent” molecule?

Dietary guidelines suggest we limit our intake of butter due to the cholesterol content and substitute oils or margarine. The following table shows the major fatty acid distribution for a typical stick of margarine and also for butter. Values are percentages.

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a. Which contains more monounsaturated fatty acids?

Dietary guidelines suggest we limit our intake of butter due to the cholesterol content and substitute oils or margarine. The following table shows the major fatty acid distribution for a typical stick of margarine and also for butter. Values are percentages.

<TABLE>

c. Which is likely to contain fewer trans-fatty acids

Are the carbon–carbon double bonds in naturally occurring fatty acids primarily cis or trans?

What is the difference in the location of the first double bond in an omega-3 and an omega-6 fatty acid (see Chemistry Link to Health “Omega-3 Fatty Acids in Fish Oils”)?

 Identify each of the following as a saturated, monounsaturated, polyunsaturated, omega-3, or omega-6 fatty acid: (15.2)

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Describe some similarities and differences in the structures of a saturated fatty acid and an unsaturated fatty acid.

Draw the line-angle formula for each of the following fatty acids:

a. palmitic acid

For each of the following fatty acids, give the shorthand notation for the number of carbon atoms and double bonds, and classify as saturated, monounsaturated, or polyunsaturated:

a. lauric acid

For each of the following fatty acids, give the shorthand notation for the number of carbon atoms and double bonds, and classify as saturated, monounsaturated, or polyunsaturated:

a. linoleic acid

How does the structure of a fatty acid with a cis double bond differ from the structure of a fatty acid with a trans double bond?

How does the double bond influence the dispersion forces that can form between the hydrocarbon chains of fatty acids?

Compare the structures and functional groups of arachidonic acid and prostaglandin PGE₁.

What are some effects of prostaglandins in the body?

How does an anti-inflammatory drug reduce inflammation?

Sunflower seed oil can be used to make margarine. A triacylglycerol in sunflower seed oil contains two linoleic acids and one oleic acid. (15.2, 15.3, 15.5) <IMAGE>

b. Using one of the isomers, write the reaction that takes place when sunflower seed oil is used to make solid margarine.

Draw the skeletal structure and give the name and omega number of the following fatty acid: CH₃CH₂CH₂CH₂CH₂HC=CHCH₂HC= CHCH₂CH₂CH₂CH₂CH₂CH₂CH₂COOH

Certain omega-3 fatty acids can be found only in animal sources, such as fatty fish. Two of these are eicosapentaenoic acid (EPA) [20:5] and docosahexaenoic acid (DHA) [22:6], both of which are ω-3 fatty acids. DHA has been shown to be important in healthy brain development, so it has recently been added to infant formulas. Breast milk is rich in DHA as long as the mother maintains a healthy diet that includes fish. Draw skeletal structures of the fatty acids EPA and DHA.

The most prevalent fatty acid in coconut oil is lauric acid, a saturated fatty acid containing 12 carbons. Draw lauric acid in skeletal structure.

Draw the condensed structural formula and skeletal structure of the saturated fatty acid with 16 carbon atoms. What is the name of this fatty acid?