Question

The wrong statement(s) among the following is/are (a) Glucose does not react with Grignard reagents. (b) Hydrolysis of maltose can be called inversion of sugar. (c) Amylopectin gives blue colour with iodine. (d) Ribose is an aldopentose.

Short answer

The wrong statement among the given options is: (b) Hydrolysis of maltose can be called inversion of sugar.

Step-by-step solution

Option (a) Glucose does not react with Grignard reagents.

Glucose is an aldehyde (an aldohexose) that contains a carbonyl group (C=O), which can react with Grignard reagents. Grignard reagents are organometallic compounds (RMgX, where R is an alkyl or aryl group and X is a halogen), which can act as strong nucleophiles and form carbon-carbon bonds. However, glucose is protected due to the presence of its hemiacetal structure, which prevents it from reacting with Grignard reagents. Therefore, this statement is correct.

Option (b) Hydrolysis of maltose can be called inversion of sugar.

Inversion of sugar refers to the process by which sucrose, a disaccharide, is hydrolyzed to form an equimolar mixture of glucose and fructose, which are monosaccharides. Maltose, on the other hand, is another type of disaccharide that is composed of two glucose units. When maltose is hydrolyzed, it produces two glucose molecules, not an equimolar mixture of glucose and fructose. Thus, the hydrolysis of maltose cannot be called inversion of sugar. This statement is incorrect.

Option (c) Amylopectin gives blue color with iodine.

Amylopectin is a branched polymer of glucose and is a major component of starch. When amylopectin is treated with iodine, the helical structure of amylopectin traps the iodine molecules, and the complex formed absorbs light in the visible region, resulting in the appearance of a blue color. This is a well-known characteristic reaction of amylopectin. Hence, this statement is correct.

Option (d) Ribose is an aldopentose.

Ribose is a monosaccharide with a molecular formula of C5H10O5, which means it contains five carbon atoms in its structure. An aldopentose is a monosaccharide containing five carbons, one of which is an aldehyde. Ribose has an aldehyde functional group in its structure, making it an aldopentose. Thus, this statement is correct. Conclusion: Among the given statements, option (b) is incorrect.

Key concepts

Carbohydrates

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen. These molecules are often referred to as sugars and are crucial for energy storage in living organisms. Carbohydrates can be classified as either mono-, di-, or polysaccharides based on the number of sugar units they contain.
Maltose, a disaccharide, is composed of two glucose molecules linked by a glycosidic bond. Upon hydrolysis, maltose releases these glucose units.
In contrast, sucrose undergoes a process called "inversion" during hydrolysis. This means that it is split into equimolar amounts of glucose and fructose, which are two different monosaccharides.
Understanding the structure and behavior of carbohydrates is vital in fields like biology and nutritional science.

Grignard Reagents

Grignard reagents are an important class of compounds in organic chemistry. These reagents are comprised of magnesium metal bonded to a halogen and an organic group (R-MgX). They are powerful nucleophiles and are commonly used to form carbon-carbon bonds by attacking electrophilic carbon atoms in carbonyl groups.
Glucose, due to its hemiacetal structure, doesn't easily react with Grignard reagents. The hemiacetal structure protects the carbonyl carbon in glucose, making it less accessible to the nucleophilic attack of a Grignard reagent.
This protection is a key reason why glucose doesn't participate in reactions with Grignard reagents under normal conditions.

Iodine Reaction with Starch

Starch is a mixture of two polymers: amylose and amylopectin. Both polymers are composed of glucose but differ in structure. The reaction between iodine and starch is a classic experiment in chemistry. When iodine is added to starch, specifically to amylose, it results in a deep blue color. This happens because the iodine molecules fit inside the helical structure of amylose, forming a complex that yields the distinctive color.
Amylopectin, which is a branched polymer, also forms a starch-iodine complex but with slight variations in color intensity due to its structure compared to amylose.
This reaction is often used as a qualitative test for the presence of starch.

Monosaccharides and Disaccharides

Monosaccharides are the simplest form of carbohydrates and consist of a single sugar unit. Common examples include glucose, fructose, and ribose. Ribose, for instance, is classified as an aldopentose, indicating it contains five carbon atoms and an aldehyde group.
Disaccharides, on the other hand, consist of two monosaccharide units linked by a glycosidic bond. Examples include sucrose and maltose. During the hydrolysis of disaccharides, the glycosidic bond is broken, yielding monosaccharides.
The structural difference between monosaccharides and disaccharides affects their chemical properties and biological functions, which is fundamental in the study of biochemistry.