Problem 128 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

Pick out the unsaturated fatty acid from the following: KCET 2004] (a) stearic acid (b) lauric acid (c) olcic acid (d) palmitic acid

Step-by-Step Solution

Answer

The unsaturated fatty acid is oleic acid (option c).

Step 1: Introduction to Fatty Acids

Fatty acids are carboxylic acids with long aliphatic chains, which can be either saturated or unsaturated. Saturated fatty acids have no double bonds between carbon atoms, while unsaturated fatty acids have one or more double bonds.

Step 2: Identifying Types of Fatty Acids

Look at the options given: - Stearic acid and lauric acid are known to be saturated as they have no carbon-carbon double bonds. - Oleic acid is an unsaturated fatty acid, commonly known to have one double bond (monounsaturated). - Palmitic acid is saturated with no double bonds.

Step 3: Picking the Unsaturated Fatty Acid

Based on the identification of fatty acids in Step 2, oleic acid is the only one with a double bond, classifying it as the unsaturated fatty acid among the options. Hence, the correct answer is oleic acid.

Key Concepts

Fatty Acids

Fatty acids are essential building blocks of fats in our body and diet. They are composed of long hydrocarbon chains ending with a carboxyl group \((-COOH)\). This structure gives them the name "carboxylic acids." The long chains of carbon atoms can be filled entirely by single bonds or can contain one or more double bonds.

• Saturated fatty acids: These have no double bonds in their chain. Think of them as having hydrogen atoms filling every possible bond to carbon.
• Unsaturated fatty acids: These contain one or more double bonds, introducing concepts such as "monounsaturated" and "polyunsaturated."

We encounter fatty acids in various forms such as oils, fats, and even some waxes. They are crucial not only for energy but also for constructing cell membranes and signaling pathways.

Saturated Fatty Acids

Saturated fatty acids have a straightforward structure that makes them distinct. In these acids, every carbon atom is single-bonded to another carbon and is fully "saturated" with hydrogen atoms. This lack of double bonds affects their properties significantly.

• Saturated fatty acids are typically solid at room temperature, which is why butter and lard maintain their shape.
• Their linear chain allows them to pack closely in a neat, uniform pattern, contributing to their solidity.

Common saturated fatty acids include stearic acid, lauric acid, and palmitic acid. While they provide important energy reserves, consuming them in excessive amounts can lead to health issues like cardiovascular disease.

Carboxylic Acids

Carboxylic acids contain a distinctive carboxyl group \((-COOH)\) that is critical for their chemical behavior. This functional group is polar, leading to the overall solubility of these compounds in water.

• The carboxyl group consists of a carbon double-bonded to an oxygen and single-bonded to a hydroxyl group.
• This arrangement makes them acidic, capable of donating a hydrogen ion \((H^+)\) to solutions, which is why they can participate in a variety of chemical reactions.

In fatty acids, the carboxylic group is at the end of a long carbon chain, which can be either saturated or unsaturated. The properties dictated by the carboxyl group and the hydrocarbon chain explain much of the fatty acid’s behavior in both biological and chemical environments.