Fatty acid Chain length Double bonds Steric 18 0 Oleic 18 1 Linoleic 18 2 Based
ID: 30910 • Letter: F
Question
Fatty acid Chain length Double bonds Steric 18 0 Oleic 18 1 Linoleic 18 2 Based on information shown in the table, which triglyceride would be expected to have the lowest melting point? A triglyceride that contains one oleic and two stearic fatty acids bonded to each glycerol molecule A triglyceride that contains one linoleic and two oleic fatty acids bonded to each glycerol molecule A triglyceride that contains three stearic fatty acids bonded to each glycerol molecule A triglyceride that contains one stearic, one oleic, and one linoleic fatty acid bonded to each glycerol moleculeExplanation / Answer
c- triglyceride with 3 stearic acid.
Saturated fatty acids have melting point higher than unsaturated fatty acids.Stearic acid is a sturated fatty acid.
Note that as a group, the unsaturated fatty acids have lower melting points than the saturated fatty acids.
The reason for this phenomenon can be found by a careful consideration of molecular geometries. The tetrahedral bond angles on carbon results in a molecular geometry for saturated fatty acids that is relatively linear although with zigzags. See graphic on the left.
This molecular structure allows many fatty acid molecules to be rather closely "stacked" together. As a result, close intermolecular interactions result in relatively high melting points.
On the other hand, the introduction of one or more double bonds in the hydrocarbon chain in unsaturated fatty acids results in one or more "bends" in the molecule. The geometry of the double bond is almost always a cis configuration in natural fatty acids. These molecules do not "stack" very well. The intermolecular interactions are much weaker than saturated molecules. As a result, the melting points are much lower for unsaturated fatty acids.
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