Question

The correct statement for sucrose is (A) Both rings are in pyranose form (B) Both rings are in furanose form (C) Glucose ring is in furanose and fructose rings is in pyranose form (D) Glucose ring is in pyranose and fructose ring is in furanose form

Short answer

The correct statement for sucrose is (D) Glucose ring is in pyranose and fructose ring is in furanose form.

Step-by-step solution

Understand the different forms of monosaccharides

Monosaccharides can exist in two different cyclic structures: pyranose and furanose. Pyranose is a six-membered ring structure (five carbons and one oxygen), while furanose is a five-membered ring structure (four carbons and one oxygen). In order to determine the correct statement, we need to know the structure of glucose and fructose in sucrose.

Identify the form of glucose in sucrose

Glucose is a hexose sugar, which means it has six carbon atoms. In sucrose, glucose exists as a pyranose ring, which is a six-membered ring composed of five carbon atoms and one oxygen atom. This information helps us to eliminate option (C) since glucose is not in the furanose form.

Identify the form of fructose in sucrose

Similar to glucose, fructose is also a hexose sugar with six carbon atoms. However, in sucrose, fructose exists as a furanose ring, which is a five-membered ring composed of four carbon atoms and one oxygen atom. This piece of information helps us to eliminate options (A) and (B).

Choose the correct statement

Based on Steps 2 and 3, we know that glucose exists in the pyranose form and fructose exists in the furanose form within sucrose. Thus, the correct statement is: (D) Glucose ring is in pyranose and fructose ring is in furanose form.

Key concepts

Monosaccharides

Monosaccharides are the simplest form of carbohydrates and are the building blocks for more complex sugars like disaccharides and polysaccharides. They are commonly referred to as single sugar units. Some popular examples include glucose, fructose, and galactose. Monosaccharides are crucial because they provide energy and serve as fundamental components in cellular processes.
They consist of carbon, hydrogen, and oxygen atoms, typically in a ratio of 1:2:1, and have the basic formula of \(C_nH_{2n}O_n\). They can appear in both linear forms and cyclic forms depending on their environment. Usually, the linear form undergoes an intramolecular reaction to form a ring, which is more stable in aqueous solutions.
Understanding monosaccharides is essential as it is a stepping stone to grasp more complex carbohydrate structures, like those found in sucrose. In this context, it is also key to recognize that monosaccharides can exist in both pyranose and furanose forms, adding versatility to their chemical behavior.

Pyranose and Furanose Forms

In the world of carbohydrates, pyranose and furanose refer to the two different ring forms that monosaccharides can adopt. These terms are inspired by the heterocyclic compounds pyran and furan, respectively.

• Pyranose: This structure is a six-membered ring composed of five carbon atoms and one oxygen atom. It is named after the pyran compound and is the typical form adopted by aldo-hexoses like glucose. The pyranose form provides stability and a framework for various biochemical interactions, which is why glucose is often found in this configuration.
• Furanose: A furanose structure is a five-membered ring with four carbon atoms and one oxygen atom. Named after the furan compound, the furanose form is most commonly seen in keto-hexoses like fructose. Although less stable compared to pyranose, it is biologically important in many contexts.

In the case of sucrose, the glucose unit adopts a pyranose form, while the fructose unit appears in the furanose form, making this knowledge vital to understanding the structural intricacies of sucrose.

Glucose and Fructose Rings

The structural forms of glucose and fructose are key to identifying the composition of more complex sugars like sucrose. Each of these sugars can exist in distinct ring formations based on their chemical derivations.

• Glucose: As a hexose sugar, glucose prefers the pyranose form due to the presence of an aldehyde group in its structure. In this form, five of the six carbon atoms complete the ring, stabilizing the molecule and making it optimal for biological functions.
• Fructose: Unlike glucose, fructose contains a ketone group, leading it to adopt the furanose form. This ring structure consists of four carbon atoms and an oxygen atom, making it slightly less stable than glucose's pyranose form, but it efficiently participates in stabilizing sucrose.

In sucrose, the combination of these two specific ring formations—glucose as pyranose and fructose as furanose—reflects a balanced link between stability and reactivity. Each sugar contributes uniquely, providing sucrose its characteristic properties and sweetness.