Question

This section contains multiple choice questions. Each question has 4 choices (a), (b), (c) and (d), out of which ONLY ONE is correct. Interchange between \(\alpha\) -D-glucose and \(\beta\) -D-glucose in aqueous solution to form an equilibrium mixture is called (a) isomerization (b) molecular rearrangement (c) mutarotation (d) tautomerism

Short answer

Question: Identify the correct term for the interchange between α-D-glucose and β-D-glucose in an aqueous solution to form an equilibrium mixture. Answer: Mutarotation

Step-by-step solution

Make a list of options and find the right term

The first step is to understand the definitions of the terms listed in the options given: (a) Isomerization is a process by which one molecule is transformed into another molecule that has the same atoms but has a different arrangement of atoms. (b) Molecular rearrangement refers to the process in which a molecule undergoes a structural transformation due to the migration of an atom or a group of atoms within the molecule. (c) Mutarotation is the process in which one specific rotation of a given compound changes to another specific rotation through ring opening and closing in the presence of water. (d) Tautomerism is the equilibrium between two or more isomers having the same molecular formula but different connectivity of atoms due to the migration of a proton.

Analyze the given problem

The interchange between α-D-glucose and β-D-glucose in an aqueous solution to form an equilibrium mixture involves the conversion between two forms of D-glucose that differ only in the configuration of the hydroxyl group (-OH) at the anomeric carbon atom.

Choose the correct term

Since mutarotation refers to the process that involves changing specific rotation through ring-opening and closing in the presence of water, it is the correct term for the interchange between α-D-glucose and β-D-glucose in an aqueous solution to form an equilibrium mixture. Thus, the correct answer is (c) mutarotation.

Key concepts

Isomerization

Isomerization in chemistry refers to the process by which one molecule is transformed into another molecule with the same atoms, but with a different arrangement of these atoms. This process does not involve the breaking of the main carbon chain but rather the spatial repositioning of atoms and bonds. For example, alkanes can undergo isomerization to form branched-chain isomers, which are useful in the petroleum industry to improve the octane rating of gasoline. In the context of sugars like glucose, isomerization can describe the conversion between different forms of the sugar molecule that have the same molecular formula but differ in their structure, such as linear and cyclic forms.

Molecular Rearrangement

Molecular rearrangement refers to a more profound transformation than simple isomerization. It involves the migration of an atom or group of atoms to a different location within the molecule, potentially changing the molecule's backbone. Rearrangements are often seen in reaction mechanisms and can result in a significant change in the molecule's properties. A well-known example within organic chemistry is the Wittig rearrangement, where an atom or group shifts from one carbon atom to another, leading to a change in the molecule's functional groups.

Tautomerism

Tautomerism is a special type of isomerization occurring when there is a chemical equilibrium between two or more isomers. They share the same molecular formula but have different atomic connectivities due to the migration of a proton (a hydrogen atom). This process can greatly affect the molecule's chemical properties. An illustrative case is the keto-enol tautomerism, commonly seen in carbonyl compounds, like acetoacetic acid, where the hydrogen atom move from an alpha carbon to an oxygen, forming a double bond in the process.

α-D-glucose

Glucose exists in several forms, with α-D-glucose being one of them. It is an isomer of glucose characterized by the position of the hydroxyl group (-OH) on the anomeric carbon (the carbon atom that was formerly part of the carbonyl group in the open-chain form of glucose). In α-D-glucose, the hydroxyl group on the anomeric carbon is on the opposite side (trans) of the carbon chain relative to the CH₂OH group at the far end of the molecule when drawn in the Haworth projection.

β-D-glucose

As a counterpart to α-D-glucose, β-D-glucose is another isomer in which the hydroxyl group on the anomeric carbon is on the same side (cis) as the CH₂OH group when depicted in a Haworth projection. In an aqueous solution, α-D-glucose and β-D-glucose are able to interconvert through a process known as mutarotation, where the cyclic form of glucose temporarily opens into the linear form, allowing the anomeric hydroxyl group to rotate, before closing back into a cyclic form.

Organic Chemistry

Organic chemistry is the scientific study of the structure, properties, composition, reactions, and synthesis of organic compounds, which are based on carbon atom chains and rings. It includes a vast range of compounds, including plastics, drugs, petrochemicals, food, and explosive materials. Within this field, understanding phenomena such as isomerization, molecular rearrangement, and tautomerism is fundamental because they explain how different organic molecules can have distinct properties even when composed of the identical set of atoms.

IIT JEE Chemistry

The Indian Institutes of Technology Joint Entrance Examination (IIT JEE) Chemistry section tests students' knowledge in various branches of chemistry, including organic, inorganic, and physical chemistry. Topics such as isomerization, tautomerism, and molecular rearrangement are crucial for students to master, as they are often covered in the exam through conceptual questions and problems that require an understanding of molecular structures and reaction mechanisms. Preparing for these topics requires a deep comprehension of concepts as well as practical problem-solving skills.