Question

Which of the following fatty acids is unsaturated? (a) palmitic acid; (b) oleic acid; (c) lauric acid; (d) stearic acid; (e) none of these.

Short answer

Among the listed fatty acids, oleic acid is unsaturated.

Step-by-step solution

Examine Fatty Acid Structures

Examine the structures of each of the listed fatty acids. Palmitic acid, lauric acid and stearic acid are all saturated fatty acids, which means they do not have double bonds – their structure consists only of single bonds between the carbon atoms. However, oleic acid is an unsaturated fatty acid and it has one double bond in its structure.

Key concepts

Oleic Acid

Oleic acid is a type of unsaturated fatty acid. This means it has one or more double bonds in its hydrocarbon chain. Specifically, oleic acid has one double bond, which distinguishes it from saturated fatty acids that contain only single bonds. The presence of this double bond gives oleic acid unique properties. It is found abundantly in olive oil, which is why it is often praised for its health benefits.
Unsaturated fatty acids like oleic acid tend to be liquid at room temperature, which is why olive oil is not solid like butter or lard. This feature can be attributed to the kink formed by the double bond, preventing the molecules from packing tightly together.
Oleic acid is also considered a monounsaturated fat, due to its single double bond. This sets it apart from polyunsaturated fatty acids that have multiple double bonds. Consuming monounsaturated fats can support heart health by improving cholesterol levels, and potentially reducing the risk of heart disease.

Saturated Fatty Acids

Saturated fatty acids are a type of fatty acid that has no double bonds between carbon atoms in their hydrocarbon chain. This means that each carbon atom is saturated with hydrogen atoms. Because of their chemical structure, saturated fats are usually solid at room temperature.
These types of fats are found in various animal products such as butter, cheese, and meats, as well as some plant oils like coconut and palm oil. In terms of chemical structure, common saturated fatty acids include palmitic acid, stearic acid, and lauric acid. These fatty acids are straight and able to pack closely together, unlike their unsaturated counterparts, thereby resulting in higher melting points.
While moderate consumption of saturated fats is part of a balanced diet, excessive intake has been linked to increased cholesterol levels and the risk of heart disease. Nutrition experts often recommend replacing some saturated fats with unsaturated fats to promote better health outcomes.

Double Bonds in Fatty Acids

The concept of double bonds in fatty acids is crucial in understanding the differences between saturated and unsaturated fats. A double bond occurs when two carbon atoms share two pairs of electrons, instead of just one pair as in a single bond. This creates a kink in the fatty acid chain.
The presence and number of double bonds influence important properties of fatty acids. Fatty acids with one double bond are termed 'monounsaturated', while those with multiple double bonds are called 'polyunsaturated'. These bonds disrupt the regular packing of molecules, making the fats less dense and generally liquid at room temperature.
Double bonds can also affect the stability of the fat. While double bonds create favorable properties for metabolism and health, they can also make the molecule more prone to oxidation and spoilage. Identifying and understanding the role of double bonds can help us choose healthier dietary fats, balancing stability and nutritional benefits.
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