Problem 74 - A Complete Resource Book in Chemistry for JEE Main

Question

Fucrose molecule is made up of (a) a gluco pyranose an a fructo pyranose (b) a gluco pyranose an a fructo furanose (c) a gluco furanose an a fructo pyranose (d) a gluco furanose an a fructo furanose

Step-by-Step Solution

Answer

The fucrose molecule is made up of (b) a gluco pyranose and a fructo furanose.

Step 1: Understand Fucrose

Fucrose, more commonly known as sucrose, is a disaccharide composed of two monosaccharides. It is important to identify which monosaccharides are present in fucrose.

Step 2: Identify the Components

Sucrose consists of one glucose unit and one fructose unit. Both of these monosaccharides are structural isomers, sharing the same molecular formula but differing in function.

Step 3: Determine the Structural Forms

Glucose and fructose can form different ring structures called pyranose or furanose. In sucrose, glucose is present in the pyranose (6-membered ring) form and fructose is present in the furanose (5-membered ring) form.

Step 4: Match to Options

Given the options, match the structural forms with the right choice. Glucose in sucrose is a gluco pyranose and fructose is a fructo furanose.

Key Concepts

Monosaccharides

Monosaccharides are the simplest form of carbohydrates and act as the building blocks for more complex sugars. They consist of a single sugar unit with the general formula \( C_nH_{2n}O_n \). These molecules are incredibly essential because they serve as primary energy sources for cells.
Monosaccharides are classified based on the number of carbon atoms they contain. For instance:

• Triose: three carbon atoms
• Tetrose: four carbon atoms
• Pentose: five carbon atoms
• Hexose: six carbon atoms

Glucose and fructose are two prominent examples of hexoses. Despite having the same molecular formula, \( C_6H_{12}O_6 \), they differ in structure and properties. This variability among monosaccharides plays a key role in forming distinct carbohydrates like disaccharides.

Pyranose and Furanose Rings

Monosaccharides can form cyclic structures, known as pyranose and furanose rings. This transformation primarily occurs because the aldehyde or keto group in the sugar reacts with one of its own hydroxyl groups.
A pyranose ring is a six-membered ring similar to the heterocyclic compound pyran. In glucose, this form is more stable and therefore more prevalent. Furanose rings, on the other hand, consist of five members like the compound furan, and are found in solutions like fructose.
The type of ring formed significantly affects the sugar's chemical properties and biological functions. Thus, an understanding of these structures is important when considering how sugars behave and interact in various biological contexts.

Glucose and Fructose

Glucose and fructose are both essential monosaccharides forming the backbone of important carbohydrates like sucrose. Glucose is a primary energy source and is ubiquitously used throughout cellular processes. Its pyranose form is the most stable structure.
Fructose, sweeter to taste compared to glucose, often appears within fruits. It naturally forms a furanose ring, making it structurally distinct yet functionally complementary to glucose in sucrose form.
Both glucose and fructose exemplify the principle of structural isomers, as they share a molecular formula while differing in structure. This difference profoundly affects their roles and how they are used within the body.

Structural Isomers

In chemistry, structural isomers are compounds that have the same molecular formula but differ in the connectivity of their atoms. This subtle difference can cause significant variations in chemical and physical properties.
Glucose and fructose illustrate structural isomerism perfectly. Despite both having \( C_6H_{12}O_6 \), the placement of atoms results in different functional groups: glucose has an aldehyde group while fructose includes a ketone group.
These differences lead to distinct properties and biological roles. Consequently, understanding structural isomers is crucial in fields like biochemistry, where slight variations in molecular structure can translate to major differences in function or reactivity.