Chapter 24, Problem 24.39AP

Interpretation Introduction

(a)

Interpretation:

Whether $\alpha -\text{D}-\text{glucopyranose}$ and $\beta -\text{D}-\text{glucopyranose}$ are epimers, anomers, enantiomers, diastereomers, constitutional isomers or none of the above is to be stated.

Concept introduction:

Sugars show different types of isomerism. They may be enantiomers, epimers, anomers, or diastereomers depending upon chirality and plane of symmetry in molecules. It also depends on stereochemistry of different carbons.

Answer to Problem 24.39AP

The compounds, $\alpha -\text{D}-\text{glucopyranose}$ and $\beta -\text{D}-\text{glucopyranose}$ are anomers as well as diastereomers of each other.

Explanation of Solution

The compounds, $\alpha -\text{D}-\text{glucopyranose}$ and $\beta -\text{D}-\text{glucopyranose}$ are anomers because their stereochemistry is different at anomeric carbon. Anomeric carbon is carbon $-1$ in aldose or carbon $-2$ in ketose.

They are diastereomers also as they are not mirror images of each other. The structure of both the compounds is shown below.

Figure 1

Conclusion

These two compounds are anomers as well as diastereomers as shown in Figure 1.

Interpretation Introduction

(b)

Interpretation:

Whether $\alpha -\text{D}-\text{glucopyranose}$ and $\alpha -\text{D}-\text{mannopyranose}$ are epimers, anomers, enantiomers, diastereomers, constitutional isomers or none of the above is to be stated.

Concept introduction:

Sugars show different types of isomerism between molecules. They may be enantiomers, epimers, anomers, or diastereomers depending upon chirality and plane of symmetry in molecules. It also depends on stereochemistry of different carbons.

Answer to Problem 24.39AP

The compounds, $\alpha -\text{D}-\text{glucopyranose}$ and $\alpha -\text{D}-\text{mannopyranose}$ are epimers as well as diastereomers of each other.

Explanation of Solution

Both the above structures of $\alpha -\text{D}-\text{glucopyranose}$ and $\alpha -\text{D}-\text{mannopyranose}$ are diastereomers as they are not mirror images. They are epimers as they differ in stereochemistry at carbon $-2$, $-\text{H}$ and $-\text{OH}$ bonds are present on different sides of carbon atom as shown below.

Figure 2

Conclusion

The compounds $\alpha -\text{D}-\text{glucopyranose}$ and $\alpha -\text{D}-\text{mannopyranose}$ are epimers and diastereomers as shown in Figure 2.

Interpretation Introduction

(c)

Interpretation:

Whether $\beta -\text{D}-\text{mannopyranose}$ and $\beta -\text{L}-\text{mannopyranose}$ are epimers, anomers, enantiomers, diastereomers, constitutional isomers or none of the above is to be stated.

Concept introduction:

Sugars show different types of isomerism between molecules. They may be enantiomers, epimers, anomers, or diastereomers depending upon chirality and plane of symmetry in molecules. It also depends on stereochemistry of different carbons.

Answer to Problem 24.39AP

The compounds, $\beta -\text{D}-\text{mannopyranose}$ and $\beta -\text{L}-\text{mannopyranose}$ are enantiomers as shown below.

Explanation of Solution

Sugars can be divided into two groups based on the symmetry of carbon atoms. If the molecule has asymmetric carbon atom it will have a non superimposable mirror image. The non superimposable mirror images are known as enantiomers. As the given compounds are non super imposable mirror images of each other they are enantiomers. This can be well explained by the illustrations shown below.

Figure 3

Conclusion

These two compounds $\beta -\text{D}-\text{mannopyranose}$ and $\beta -\text{L}-\text{mannopyranose}$ are enantiomers of each other as shown in Figure 3.

Interpretation Introduction

(d)

Interpretation:

Whether $\alpha -\text{D}-\text{ribofuranose}$ and $\alpha -\text{D}-\text{ribopyranose}$ are epimers, anomers, enantiomers, diastereomers, constitutional isomers or none of the above is to be stated.

Concept introduction:

Sugars show different types of isomerism between molecules. They may be enantiomers, epimers, anomers, or diastereomers depending upon chirality and plane of symmetry in molecules. It also depends on stereochemistry of different carbons.

Answer to Problem 24.39AP

The compounds, $\alpha -\text{D}-\text{ribofuranose}$ and $\alpha -\text{D}-\text{ribopyranose}$ are constitutional isomers as they have same molecular formula but different chemical structure as shown below.

Explanation of Solution

As the isomers are the compounds, having similar chemical formula but different structures. These two compounds have same chemical formula. The chemical structure is of these two compounds is quite different as shown in Figure 4.

Figure 4

In the above shown compounds, one is a pentose sugar furanose while the other is a hexose sugar pyranose.

Conclusion

These two compounds, $\alpha -\text{D}-\text{ribofuranose}$ and $\alpha -\text{D}-\text{ribopyranose}$ are constitutional isomers as shown in Figure 4.

Interpretation Introduction

(e)

Interpretation:

Whether $\text{D}-\text{Glucose}$ and $\alpha -\text{D}-\text{glucopyranose}$ are epimers, anomers, enantiomers, diastereomers, constitutional isomers or none of the above is to be stated.

Concept introduction:

Sugars show different types of isomerism between molecules. They may be enantiomers, epimers, anomers, or diastereomers depending upon chirality and plane of symmetry in molecules. It also depends on stereochemistry of different carbons.

Answer to Problem 24.39AP

Aldehyde form of $\text{D}-\text{Glucose}$ and $\alpha -\text{D}-\text{glucopyranose}$ are constitutional isomers. Their chemical structure is different but molecular formula is same as shown below.

Explanation of Solution

As the isomers are the compounds, having similar chemical formula but different structures. Both the above structures are constitutional isomers as shown below in the Figure.

Figure 5

In the above shown compounds, one is a ring structure having keto group while the other is open ring structure having aldehyde as the functional group. The chemical formula of the given compounds is same but their properties are totally different.

Conclusion

The given compounds $\text{D}-\text{Glucose}$ and $\alpha -\text{D}-\text{glucopyranose}$ are different in chemical structure and therefore their properties are different. So, they are constitutional isomers as shown in Figure 5.

Interpretation Introduction

(f)

Interpretation:

Whether the compounds, $\text{methyl}\alpha -\text{D}-\text{fructofuranoside}$ and $2-O-\text{methyl}-\alpha -\text{D}-\text{fructofuranose}$ are enantiomers. epimers, anomers, enantiomers, diastereomers, constitutional isomers or none of the above is to be stated

Concept introduction:

Sugars show different types of isomerism between molecules. They may be enantiomers, epimers, anomers, or diastereomers depending upon chirality and plane of symmetry in molecules. It also depends on stereochemistry of different carbons. The naming of the same compound can be done in different manners.

Answer to Problem 24.39AP

The compounds, $\text{methyl}\alpha -\text{D}-\text{fructofuranoside}$ and $2-O-\text{methyl}-\alpha -\text{D}-\text{fructofuranose}$ are identical compounds only the way of naming is different.

Explanation of Solution

The structure of $\text{methyl}\alpha -\text{D}-\text{fructofuranoside}$ or $2-O-\text{methyl}-\alpha -\text{D}-\text{fructofuranose}$ is shown below.

Figure 6

So, the compound is same, they are identical. In first name it is taken as methyl derivative of $\alpha -\text{D}-\text{fructofuranoside}$ as in second name methyl is taken on carbon attached to oxygen atom which is again the $\text{α}$ carbon on atom. They are identical compounds not isomers.

Conclusion

The compound shown in Figure 6 can be named as $\text{methyl}\alpha -\text{D}-\text{fructofuranoside}$ as well as $2-O-\text{methyl}-\alpha -\text{D}-\text{fructofuranose}$. Both are the name of the same structure.