Question

Which of the following compounds can be detected by Molisch's test? (a) Amines (b) Sugars (c) Nitro compounds (d) Primary alcohols

Short answer

(b) Sugars can be detected by Molisch's test.

Step-by-step solution

Understanding Molisch's Test

Molisch's test is a sensitive chemical test for the presence of carbohydrates. It is named after the Austrian botanist Hans Molisch. The test uses Molisch's reagent, a solution of alpha-naphthol in ethanol, and concentrated sulfuric acid. This test is used to detect all types of sugars, whether they are monosaccharides, disaccharides, or even polysaccharides.

Evaluating Each Option

Let's examine whether each of the given options can be detected by Molisch's test: (a) Amines: Amines do not contain carbohydrate structures; they are derivatives of ammonia, and hence do not react in Molisch's test. (b) Sugars: Sugars, which are carbohydrates, will be detected by Molisch's test. When sugars react with Molisch's reagent and sulfuric acid, a purple or violet ring is formed, indicating a positive result. (c) Nitro compounds: Nitro compounds contain nitro groups (-NO2) and do not have carbohydrate structures, so they do not give a positive Molisch's test. (d) Primary alcohols: Like amines and nitro compounds, primary alcohols do not contain carbohydrate structures, so they do not react in Molisch's test.

Identifying the Correct Answer

From the analysis, sugars are the only compounds among the options that will react positively in Molisch's test. The formation of a purple or violet ring when sugars are treated with Molisch's reagent and sulfuric acid confirms their presence.

Key concepts

Molisch's Test

Molisch's test is a classic analytical technique used in organic chemistry to detect the presence of carbohydrates. It was named after Hans Molisch, an Austrian botanist, who developed the test. This test is regarded for its sensitivity and simplicity. It involves using Molisch's reagent, which is alpha-naphthol dissolved in ethanol, and concentrated sulfuric acid to test for carbohydrates. When a substance containing carbohydrates is mixed with these reagents, a characteristic purple or violet-colored ring forms at the interface of the solution and acid layer. This color change is a positive indicator of carbohydrates being present. Molisch's test is versatile, indicating the presence of both freer and complex forms of sugars, such as monosaccharides, disaccharides, and polysaccharides.

For students studying organic chemistry, Molisch's test is foundational, as it handles a central group of biomolecules—carbohydrates—providing insights into the chemical behavior of various substances.

Carbohydrates

Carbohydrates are organic compounds consisting of carbon, hydrogen, and oxygen. They are crucial for life due to their role in energy production and storage. Carbohydrates exist in different forms, ranging from simple sugars to complex polysaccharides, and they serve as the body's primary energy source.

There are several types of carbohydrates:

• Monosaccharides: The simplest form, including glucose and fructose.
• Disaccharides: Consist of two linked monosaccharides, such as sucrose and lactose.
• Polysaccharides: Long chains of monosaccharides, like starch and cellulose.

Carbohydrates play a variety of roles beyond energy, including structural functions in cells and participating in cellular communication. Understanding carbohydrates is vital for studying their biochemical functions and how they contribute to both health and disease.

Sugars

Sugars are simple carbohydrates that are typically sweet in taste and are key components in foods and biological systems. Sugars include glucose, fructose, and sucrose, among others. These are often classified based on their structure as mono- or disaccharides. Sugars provide quick energy, as they are easily broken down into glucose during digestion.

Sugars are also important in metabolism and cellular respiration, where they undergo glycolysis for energy release. Additionally, sugars are crucial in various biochemical pathways, influencing numerous processes such as cell signaling and the synthesis of DNA and RNA. Their presence can be easily detected by Molisch's test due to their distinctive chemical properties.

Organic Chemistry Test

Organic chemistry tests, like Molisch's test, are essential for identifying and understanding the composition and properties of organic substances. Such tests provide a way to deduce chemical structures and functionalities present in a compound.

These tests often focus on specific functional groups, like carbohydrates, amines, or alcohols, and involve observable reactions that confirm the presence of these groups. For example, in the classroom or laboratory, students might use Molisch's test as a practical application to detect carbohydrates in unknown samples. Practical organic chemistry tests help students develop a hands-on understanding of chemical reactions, enhancing theoretical knowledge and problem-solving in the context of real-world chemistry.