Question

During configuration determination of D-Glucose, there was a doubt between the following Isomers. A scientist thought that following reaction sequence help to find out correct D-glucose. If $\mathrm{R}$ is also a Aldohexose different from sample, then correct configuration of D-Glucose concluded by scientist is (A) I (B) II (C) III (D) Can't differentiate between I and III

Short answer

The correct configuration of D-Glucose cannot be differentiated between Isomer I and Isomer III based on the given reaction sequence. Therefore, the answer is (D) Can't differentiate between I and III.

Step-by-step solution

Identify the characteristics of each isomer.

To find out the correct isomer, we first need to look at the characteristics of each isomer. D-Glucose, being an aldohexose, must have these characteristics: - An aldehyde functional group - A total of 6 carbon atoms - D configuration, which means the hydroxyl group (OH) is on the right side of the second to last (penultimate) carbon atom in the Fischer projection

Analyze each isomer with the reaction sequence for D-Glucose characteristics.

Following the reaction sequence, let's check each isomer one by one. - Isomer I: The aldehyde functional group is present in Isomer I, and it has 6 carbon atoms. The hydroxyl group (OH) is on the right side of the second to last (penultimate) carbon atom in the Fischer projection. Therefore, all characteristics match with D-Glucose. - Isomer II: The aldehyde functional group is present in Isomer II, and it has 6 carbon atoms. However, the hydroxyl group (OH) is on the left side of the second to last (penultimate) carbon atom in the Fischer projection. It does not have the D configuration. - Isomer III: The aldehyde functional group is present in Isomer III, and it has 6 carbon atoms. The hydroxyl group (OH) is on the right side of the second to last (penultimate) carbon atom in the Fischer projection. Therefore, all characteristics match with D-Glucose.

Conclusion.

Based on the analysis, Isomer I and Isomer III both match with the D-Glucose characteristics. However, the given reaction sequence does not differentiate between Isomer I and Isomer III. So, the correct answer is (D) Can't differentiate between I and III.

Key concepts

Aldohexose

An aldohexose is a type of sugar that features six carbon atoms and an aldehyde group typically at the first carbon atom. In biochemistry, these sugars play crucial roles, particularly in energy metabolism. D-Glucose, a common dietary sugar, is one such aldohexose.

Key characteristics of aldohexoses include the following:

• They consist of a chain of six carbon atoms (hence 'hex' in the name).
• The aldehyde functional group is located at the end of the molecule (carbon-1).
• They are classified based on their stereochemistry, which refers to the spatial arrangement of atoms and the impact of this arrangement on the molecule's properties.
• Aldohexoses can exist in 'D' or 'L' forms; these forms are mirror images of each other, similar to left and right hands.

In solving configuration problems, identifying the sugar type and its functional groups is the first step.

Fischer projection

Fischer projections are a method of illustrating the three-dimensional structures of molecules on a two-dimensional plane. They're particularly useful in biochemistry for representing the stereochemistry of carbohydrates.

In a Fischer projection:

• The vertical lines represent bonds that project away from the viewer or into the plane of the page.
• The horizontal lines represent bonds that project out of the plane of the page, towards the viewer.
• Carbon atoms are not explicitly shown at each intersection of vertical and horizontal lines, but it's understood that they exist there.
• The most oxidized group, often the aldehyde or carboxyl group in sugars, is traditionally at the top.
• For molecules like sugars, the bottom carbon atom is often the carbon nearest to the end of the molecule opposite the most oxidized group.

When working with Fischer projections, comparing the positions of hydroxyl groups (-OH) can help determine the D or L configuration of the molecules, which is an integral part of their identity and function.

Stereochemistry

Stereochemistry is the subdiscipline of chemistry that involves the study of the relative spatial arrangement of atoms within molecules and how this arrangement affects their chemical properties and reactions.

Key concepts in stereochemistry include:

• Chirality: This refers to the property of a molecule having a non-superimposable mirror image. Chiral molecules are often referred to as being 'handed', with the terms 'left-handed' (L) and 'right-handed' (D) indicating the orientation of certain substituents around a chiral center.
• Enantiomers: These are pairs of molecules that are mirror images of each other but cannot be overlaid, much like left and right hands. Enantiomers often have very different biological activities.
• Diastereomers: These are isomers that have opposite configurations at one or more of the chiral centers but are not mirror images.
• Epimers: A specific type of diastereomers that differ in configuration at exactly one chiral center.

Stereochemistry is essential to understanding molecules like D-glucose because the function of these molecules in biological systems depends on their precise 3D arrangement.