Chapter 7, Problem 1P

Answers to all problems are at the end of this book. Detailed solutions are available in the Student Solutions Manual, Study Guide, and Problems Book.

Drawing Haworth Structures of Sugars Draw Haworth structures for the two possible isomers of D-altrose (Figure 7.2) and D-psicose (Figure 7.3).

Interpretation Introduction

Interpretation: The Haworth structures for two possible isomers of $\text{D}-\text{altrose}$ and $\text{D}-\text{psicose}$ are to be drawn.

Concept introduction: The simplest hydrolyzed form that is obtained from the carbohydrates is known as a monosaccharide.

Haworth projection is a method that is used to provide the three-dimensional cyclic form of a monosaccharide. This method shows the monosaccharide in the form of a hemiacetal ring or hemiketal ring.

Carbon atom which behaves as a stereocenter or a chiral center in the cyclic ring form of the hemiacetal or hemiketal compound is known as anomeric carbon.

Answer to Problem 1P

The Haworth structures for two possible isomers of $\text{D}-\text{altrose}$ and $\text{D}-\text{psicose}$ are shown below.

  

Explanation of Solution

The anomeric carbon of a monosaccharide unit always possesses two types of isomers. One is $\alpha -$ isomer in which the hydroxyl $\left(-\text{OH}\right)$ group is located below the plane of the ring and the second is $\beta -$ isomer in which the hydroxyl $\left(-\text{OH}\right)$ group is located above the plane of the ring.

The molecular formula of $\text{D}-\text{altrose}$ is ${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6}}$ . The two possible isomers of $\text{D}-\text{altrose}$ are $\alpha -\text{D}-\text{altrose}$ and $\beta -\text{D}-\text{altrose}$ . The Haworth structures for two possible isomers of $\text{D}-\text{altrose}$ are shown below.

  

  Figure 1

In the Haworth projection of $\alpha -\text{D}-\text{altrose}$ , the hydroxyl $\left(-\text{OH}\right)$ group which is present at the anomeric carbon is located below the plane of the cyclic ring. On the other hand, in $\beta -\text{D}-\text{altrose}$ , the hydroxyl $\left(-\text{OH}\right)$ group which is present at the anomeric carbon located above the plane of the cyclic ring.

The molecular formula of $\text{D}-\text{psicose}$ is ${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6}}$ . The two possible isomers of $\text{D}-\text{psicose}$ are $\alpha -\text{D}-\text{psicose}$ and $\beta -\text{D}-\text{psicose}$ . The Haworth structures for two possible isomers of $\text{D}-\text{psicose}$ are shown below.

  

  Figure 2

In the Haworth projection of $\alpha -\text{D}-\text{psicose}$ , the hydroxyl $\left(-\text{OH}\right)$ group which is present at the anomeric carbon is located below the plane of the cyclic ring. On the other hand, in $\beta -\text{D}-\text{psicose}$ , the hydroxyl $\left(-\text{OH}\right)$ group which is present at the anomeric carbon is located above the plane of the cyclic ring.