Problem 56 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

Glucose cannot be classified as: (a) aldose (b) carbohydrate (c) hexose (d) oligosaccharide

Step-by-Step Solution

Answer

The correct answer is (d) oligosaccharide.

Step 1: Analyze the Options

Consider each provided option and understand the terms. Glucose is a sugar and we need to determine which category it does not belong to. (a) An **aldose** is a monosaccharide that contains an aldehyde group. (b) A **carbohydrate** is an organic compound consisting of carbon, hydrogen, and oxygen, commonly known as sugars and starches. (c) A **hexose** is a six-carbon molecule, and glucose has six carbon atoms. (d) An **oligosaccharide** is a carbohydrate made up of a small number (typically two to ten) of monosaccharide units.

Step 2: Identify Glucose Characteristics

Glucose is indeed an aldose, as it contains an aldehyde group in its structure. It is also a carbohydrate because it consists of carbon, hydrogen, and oxygen atoms in a specific ratio, fitting the general definition. Furthermore, glucose is specifically a hexose because it is a six-carbon sugar. Glucose is not an oligosaccharide because it is made up of only one sugar unit, making it a monosaccharide, not a multiple-unit sugar.

Step 3: Conclude the Classification

Based on the above analysis, glucose can be classified as an aldose (a), a carbohydrate (b), and a hexose (c). However, it cannot be classified as an oligosaccharide (d) as it is a single sugar unit and not a compound made of multiple monosaccharide units.

Key Concepts

Aldose

Glucose belongs to a special group of sugars known as aldoses. Aldoses are a type of monosaccharide, which are the simplest form of carbohydrates. They contain a distinctive functional group called an aldehyde, which is responsible for specific chemical properties.

• The aldehyde group in an aldose means that the sugar has a double-bonded oxygen atom connected to the terminal carbon atom.
• Aldoses play a vital role in our metabolism and serve as fundamental building blocks in the structure of other carbohydrates.

Understanding aldoses is crucial for recognizing how glucose functions within our bodies and how it fits into broader categories of carbohydrates. The presence of an aldehyde functional group immediately classifies glucose within this group. Furthermore, this classification helps in predicting the chemical behavior and reactivity of glucose.

Hexose

Glucose is also classified as a hexose, which simply means it is a sugar with six carbon atoms. The term "hexose" comes from "hex-" indicating six and "-ose" used for sugars.

• Hexoses are crucial because they are the building blocks of many essential carbohydrates.
• The six-carbon structure influences the physical properties and reactivity of glucose.

Additionally, the arrangement of atoms in glucose as a hexose is optimal for energy storage and release, making it a critical energy source for living organisms. This classification as a hexose is significant because it distinguishes certain chemical properties and uses, especially in biological systems.

Monosaccharide vs Oligosaccharide

One significant classification is understanding the difference between monosaccharides and oligosaccharides. Glucose is a perfect example of a monosaccharide.

• Monosaccharides are fundamental sugars that cannot be broken down into simpler sugars. They are simple sugars, and glucose is one of them.
• In contrast, oligosaccharides consist of a few monosaccharide units linked together, ranging typically from two to ten units.

Glucose, being a monosaccharide, functions as a basic energy source that cells can readily use. Its simplicity allows it to be quickly absorbed and processed by the body. Understanding this distinction between a single-unit sugar like glucose and multi-unit oligosaccharides is key in grasping how carbohydrates vary in complexity and function.