Question

Draw the skeletal formula of the following fatty acids: a. palmitic acid b. oleic acid

Short answer

Palmitic acid: a zigzag line with 15 carbons plus one carboxyl group. Oleic acid: similar, but with a double bond between the 9th and 10th carbons.

Step-by-step solution

Understand the Structure of Palmitic Acid

Palmitic acid is a saturated fatty acid, meaning it has no double bonds in its hydrocarbon chain. It has 16 carbon atoms in its chain (C16:0), with a carboxyl group (-COOH) at one end.

Draw the Skeletal Formula of Palmitic Acid

To draw the skeletal formula, start with the carboxyl group at one end. Then draw a zigzag line representing the 15 remaining carbon atoms in the chain (since one carbon is in the carboxyl group). Avoid drawing hydrogen atoms.

Understand the Structure of Oleic Acid

Oleic acid is an unsaturated fatty acid. It has one double bond in its hydrocarbon chain. It contains 18 carbon atoms in total (C18:1), with the double bond typically located between the 9th and 10th carbons from the carboxyl group.

Draw the Skeletal Formula of Oleic Acid

Start by drawing the carboxyl group. Draw a zigzag line for the first 8 carbon atoms. Indicate the double bond with a double line (two parallel lines) between the 9th and 10th carbons. Continue the zigzag line for the remaining 8 carbon atoms, making sure to end with single bonds.

Key concepts

palmitic acid structure

Palmitic acid, also known as hexadecanoic acid, is a saturated fatty acid. This means it has no double bonds between the carbon atoms in its chain. It has a straight-chain structure with 16 carbon atoms (indicated as C16:0). The term 'saturated' refers to the fact that the carbon atoms are fully bonded with hydrogen atoms. On one end of the chain, palmitic acid has a carboxyl group (-COOH), making it an organic acid. To draw its skeletal formula, start with the carboxyl group and then draw 15 carbon atoms in a zigzag line connected by single bonds, representing the hydrocarbon chain. Leave out the hydrogen atoms as they are implied.

oleic acid structure

Oleic acid is a common monounsaturated fatty acid. This means that there is a single double bond in the hydrocarbon chain. Oleic acid consists of 18 carbon atoms (C18:1). The double bond in oleic acid is most commonly found between the 9th and 10th carbon atoms from the carboxyl group, which is why it is termed (9Z)-octadec-9-enoic acid. The 'Z' notation indicates the cis configuration of the double bond, meaning the hydrogen atoms adjacent to the double bond are on the same side. To draw oleic acid's skeletal formula, begin with the carboxyl group, then draw a zigzag line for the first eight carbon atoms. A double line, representing the double bond, should connect the 9th and 10th carbons. After that, continue with a zigzag for the remaining eight carbons, ending with single bonds.

saturated vs unsaturated fatty acids

Fatty acids can be categorized into saturated and unsaturated based on the presence or absence of double bonds in their hydrocarbon chains.

• Saturated Fatty Acids: These fatty acids have no double bonds between the carbon atoms. Each carbon atom is fully 'saturated' with hydrogen atoms. Examples include palmitic acid and stearic acid. Their straight-chain structure allows them to pack closely together, making them solid at room temperature, like butter.
• Unsaturated Fatty Acids: These have one (monounsaturated) or more (polyunsaturated) double bonds in their chain. The presence of double bonds, especially in the cis configuration, introduces kinks, preventing the molecules from packing tightly. This results in a liquid state at room temperature, like olive oil. Examples include oleic acid (monounsaturated) and linoleic acid (polyunsaturated).

Understanding the differences between these types of fatty acids is essential for studying their properties and roles in nutrition and biology.