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Q.11.

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Organic Chemistry
Found in: Page 393

Short Answer

Question: Linolenic acid (Table 10.2) and stearidonic acid are omega-3 fatty acids, unsaturated fatty acids that contain the first double bond located at C3, when numbering begins at the methyl end of the chain. Predict how the melting point of stearidonic acid compares with the melting points of linolenic and stearic acids. A current avenue of research is examining the use of soybean oil enriched in stearidonic acid as a healthier alternative to vegetable oils that contain fewer degrees of unsaturation.

Answer

Srearidonic acid has the lowest melting point, linolenic acid has the intermediate melting point, and stearic acid has the highest melting point.

See the step by step solution

Step by Step Solution

Step 1: Melting point of alkenes

Melting point is the temperature at which the solid and the liquid state of a substance co-exist at equilibrium.

Step 2: Factors affecting melting point

The melting point depends on the following:

  • Close-packing of the substance: The tighter the packing, the higher will be the melting point.
  • Size of molecules: The bigger the molecule, the higher will be the melting point.
  • Hydrogen-bond: The substance having the ability to form a hydrogen bond have higher melting points.
  • Double bond: The more the number of hydrogen bonds, the lower will be the melting point. Cis alkenes have a lower melting point than trans alkenes.

Step 3: Drawing the structures of the given compounds

The double bonds decrease the melting point of a substance.

Stearidonic acid has four double bonds, linolenic acid has three double bonds, and stearic acid does not have any double bonds. Thus, stearidonic acid has the lowest melting point, linolenic acid has an intermediate melting point, and stearic acid has the highest melting point.

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