Label the fatty acids below with the following information: a) Saturated or unsaturated. b) If the fatty acid is unsaturated, also label if it is a monounsaturated or polyunsaturated fatty acid. H? H? H? H? H? H? H? H? 3. H?C C C C C C C C C-OH H? H? H? H? H? H? H? H? H? H? H H H H H? H? H? O 2. H?C C C C=C C C C C-OH H? H? H? H? H? H? H? H? H? H? H H H H H? H? H? O 1. H?C C C=C C=C C C C C-OH H? H? H? H? H? H? H? H? 11. Which of the three fatty acids from #10 above would be solid at biological temperatures? a) Circle all that apply: 1. 2. 3. b) Why is it solid?
The Correct Answer and Explanation is:
Fatty Acid Identification:
1. Structure: H₃C–CH₂–CH=CH–CH=CH–CH₂–CH₂–CH₂–COOH
- a) Unsaturated
- b) Polyunsaturated (contains two double bonds)
2. Structure: H₃C–CH₂–CH₂–CH=CH–CH₂–CH₂–CH₂–COOH
- a) Unsaturated
- b) Monounsaturated (contains one double bond)
3. Structure: H₃C–CH₂–CH₂–CH₂–CH₂–CH₂–CH₂–CH₂–COOH
- a) Saturated (contains no double bonds)
11. Which fatty acids would be solid at biological temperatures?
a) Circle all that apply:
3
b) Why is it solid?
Fatty acid 3 is solid at biological temperatures because it is a saturated fatty acid. Saturated fatty acids do not contain any double bonds between the carbon atoms in their hydrocarbon chains. This straight structure allows the molecules to pack closely together in a regular, orderly fashion. The tight packing increases intermolecular forces, primarily van der Waals interactions, which raises the melting point of the substance. As a result, saturated fats are typically solid at room and body temperatures.
In contrast, unsaturated fatty acids, such as those in fatty acids 1 and 2, contain one or more double bonds. These double bonds usually exist in the cis configuration, which introduces kinks into the hydrocarbon chain. These kinks disrupt the regular packing of molecules, weakening intermolecular forces and lowering the melting point. As a result, unsaturated fats are usually liquid at biological temperatures.
Fatty acid 1, being polyunsaturated, has even more bends due to its multiple double bonds, making it the most fluid of the three. Fatty acid 2 is monounsaturated and slightly less fluid but still liquid under physiological conditions. Therefore, only fatty acid 3, with its fully saturated and straight chain, remains solid and is typically found in animal fats and some tropical oils.
