Question

If \(\mathrm{C}-5\) carbon of \(\mathrm{D}-\) glucose is inverted the new compound is related to the parent compound as (a) Enantiomer (b) Epimer (c) Anomer (d) diastereomer

Short answer

The new compound is an epimer of D-glucose.

Step-by-step solution

Understand the Structure of D-Glucose

D-glucose is an aldose sugar with six carbon atoms labeled C-1 through C-6. The hydroxyl (OH) groups on each carbon decide its stereoisomeric form. Specifically, C-5 in D-glucose has the OH group on the right in a Fischer projection.

Inversion at C-5

Inverting the configuration at C-5 means changing the position of the OH group from the right side to the left in a Fischer projection. This inversion changes the stereochemistry only at this position, creating a different isomer.

Define the Term 'Epimer'

An epimer is a type of diastereomer where the two carbohydrates differ only at one carbon atom. In this context, an epimer of D-glucose differs only at the C-5 position.

Identify the Correct Relationship

Since the inversion at C-5 changes only that particular carbon's stereochemistry with respect to D-glucose, the new sugar and D-glucose are epimers.

Key concepts

D-glucose

D-glucose is a fundamental sugar in carbohydrate chemistry and plays a crucial role in biology. As an aldose sugar, D-glucose features an aldehyde group, which is evident at the first carbon (C-1) in its structure. The molecular formula for glucose is \( ext{C}_6 ext{H}_{12} ext{O}_6\). This sugar is a hexose, meaning it contains six carbon atoms numbered from C-1 to C-6. In the context of stereochemistry, D-glucose is defined by the orientation of its hydroxyl (OH) groups attached to these carbon atoms. Specifically, in its most common projection (known as the Fischer projection), the hydroxyl group on the fifth carbon (C-5) is prominent and helps determine its classification as D-glucose due to its position on the right side. This orientation is pivotal for D-glucose's biological function, influencing how it interacts with enzymes and other biomolecules. D-glucose is ubiquitous in nature, serving as a primary energy source for cells through pathways like glycolysis and cellular respiration.

Stereoisomerism

Stereoisomerism in chemistry refers to the spatial arrangement of atoms in molecules that have the same molecular formula. This means that even if the sequence of atoms is identical, the way they are oriented in space differs between stereoisomers. In carbohydrates, like glucose, stereoisomerism is crucial. The distinct placement of OH groups at various carbon atoms leads to different sugars. Each unique arrangement yields stereoisomers that can greatly affect a sugar's properties and behavior. There are two main types of stereoisomerism:

• Enantiomerism: This involves isomers that are mirror images of each other. They are non-superimposable, similar to left and right hands.
• Diastereomerism: This includes isomers that are not mirror images of each other. Diastereomers differ at one or more stereocenters.

Understanding stereoisomerism is important when studying biochemical processes as even a single change in configuration can lead to dramatically different biological roles and activities.

Epimer

An epimer is a special type of stereoisomer that defines in particular the relationship between certain carbohydrates. Two carbohydrates are epimers if they differ only at one single carbon atom's stereochemistry. This is a relatively small change but can have significant implications. For example, in D-glucose, when the hydroxyl group configuration at C-5 is flipped, the resulting molecule is referred to as an epimer of D-glucose. Importantly, while epimers belong to the larger class of diastereomers, they are distinguished by their difference at only one carbon position. Understanding epimers is essential in fields like pharmacology and biochemistry, where even minuscule variations in structure can alter the functionality and interaction of molecules in living organisms.

Fischer Projection

The Fischer projection is a method for depicting three-dimensional molecules in two dimensions. Conceived by Emil Fischer, this system facilitates the representation of carbohydrates, such as glucose, on a flat surface. In the Fischer projection, the molecule is oriented vertically with the longest carbon chain, and the most oxidized carbon at the top, usually C-1. The horizontal lines represent bonds projecting out of the plane, while vertical lines stand for bonds going behind the plane. For sugars like D-glucose, the Fischer projection shows the configuration of hydroxyl ( OH) groups at each carbon. Specifically, at C-5, the OH group on the right identifies it as the D-enantiomer. The simplicity of the Fisher projection makes it an invaluable tool for chemists. It provides a clear view of stereochemistry, enabling easier understanding of isomer relationships and interactions.