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12: Lipids

Students classify lipids by type (fatty acids, triacylglycerols, sphingolipids, steroids, waxes), identify lipid structures from molecular formulas, and distinguish saturated from unsaturated fatty acids.

LibreTexts reference: Unit 3, Chapter 3: Lipids LibreTexts

Fatty Acid Delta Positions from Structures

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A polyunsaturated fatty acid with 19 carbons is described by the notation Δ–3,11,15. Each candidate structure below shows a skeletal zigzag with the methyl end on the left (H3C) and the carboxyl end on the right (COOH); each vertex and line end represents one carbon atom.
Which structure correctly matches the Δ–3,11,15 notation?

 

Fatty Acid Omega Notations from Structures

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A polyunsaturated fatty acid with 21 carbons is described by the notation ω–4,8,17. Each candidate structure below shows a skeletal zigzag with the methyl end on the left (H3C) and the carboxyl end on the right (COOH); each vertex and line end represents one carbon atom.
Which structure correctly matches the ω–4,8,17 notation?

 

Fatty Acid Double-Bond Positions in Delta Notation

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H3C/\/\/\/\/\/\‗/\‗/\/COOH
The skeletal structure above shows an unsaturated fatty acid with 20 carbons. The methyl end is on the left (H3C) and the carboxyl end (COOH) is on the right. Each vertex and line end represents one carbon atom. Δ (Delta) notation counts carbons from the COOH end (carbon 1).
What is the correct Δ (Delta) notation describing the positions of the double bonds in this 20-carbon fatty acid?

 

Fatty Acid Double-Bond Positions in Omega Notation

Click to show Fatty Acid Double-Bond Positions in Omega Notation example problem

H3C/\/\/\/═\/═\/\/\/\‗/COOH
The skeletal structure above shows an unsaturated fatty acid with 21 carbons. The methyl end is on the left (H3C) and the carboxyl end (COOH) is on the right. Each vertex and line end represents one carbon atom.
What is the correct ω (omega) notation describing the positions of the double bonds in this 21-carbon fatty acid?

 

Fatty Acid Chain Length and Number of Double Bonds

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The notation 18:3 indicates which of the following about a fatty acid?
 

Lipids by Molecular Formula

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Based on only their molecular formula, which one of the following compounds is most likely a lipid?