Chapter 18, Problem 18.73P

Interpretation Introduction

(a)

Interpretation:

The Haworth projection for given molecule is to be drawn.

Concept introduction:

Structural drawings of carbohydrates in cyclic forms are called Haworth formulas. The $\text{CH=O}$ functional group is converted to a hemiacetal where the carbonyl carbon becomes a new asymmetric carbon called anomeric carbon. Two types of cyclic forms can be drawn – one is pyranose, having six membered ring with one oxygen, and furanose, having five membered ring with one oxygen. For the pyranose, the hydroxyl group at C-5 forms a bond with $\text{CH=O}$ group, and for furanose, the hydroxyl group at C-4 forms a bond with $\text{CH=O}$ group. In a Fischer projection, the substituents to the right are down, and those to the left are up in the corresponding Haworth formula. For the $\text{D}$ series of carbohydrates, if the hydroxyl group at anomeric carbon is down, the configuration at that carbon is $\text{α}$, and if the hydroxyl group is up, the configuration at anomeric carbon is $\text{β}$.

Answer to Problem 18.73P

The Haworth projection of $\text{α-D-allopyranose}$ is

Explanation of Solution

The given molecule is $\text{α-D-allopyranose}$.

The structure of $\text{α-D-allopyranose}$ can be drawn from the Fischer projection of $\text{D-allose}$. The Fischer projection of $\text{D-allose}$ is

The name $\text{α-D-allopyranose}$ suggests that the ring must be six membered, where the hydroxyl group at anomeric carbon must be down. Thus the hydroxyl group at C-5 attacks the $\text{CH=O}$ group from up side. The mechanism for the cyclization of $\text{D-allose}$ to its $\text{α-D-allopyranose}$ form is

Conclusion

The Haworth projection of $\text{α-D-allopyranose}$ is drawn with six membered ring, indicating appropriate stereochemistry and placing the hydroxyl group down at anomeric carbon.

Interpretation Introduction

(b)

Interpretation:

The Haworth projection for given molecule is to be drawn.

Concept introduction:

Structural drawings of carbohydrates in cyclic forms are called Haworth formulas. The $\text{CH=O}$ functional group is converted to a hemiacetal where the carbonyl carbon becomes a new asymmetric carbon called anomeric carbon. Two types of cyclic forms can be drawn – one is pyranose, having six membered ring with one oxygen, and furanose, having five membered ring with one oxygen. For the pyranose, the hydroxyl group at C-5 forms a bond with $\text{CH=O}$ group, and for furanose, the hydroxyl group at C-4 forms a bond with $\text{CH=O}$ group. In a Fischer projection, the substituents to the right are down, and those to the left are up in the corresponding Haworth formula. For the $\text{D}$ series of carbohydrates, if the hydroxyl group at anomeric carbon is down, the configuration at that carbon is $\text{α}$, and if the hydroxyl group is up, the configuration at anomeric carbon is $\text{β}$.

Answer to Problem 18.73P

The Haworth projection of $\text{α-D-allopyranose}$ is

Explanation of Solution

The given molecule is $\text{β-D-allopyranose}$.

The structure of $\text{β-D-allopyranose}$ can be drawn from the Fischer projection of $\text{D-allose}$. The Fischer projection of $\text{D-allose}$ is

The name $\text{β-D-allopyranose}$ suggests that the ring must be six membered where the the hydroxyl group at anomeric carbon must be up. Thus, the hydroxyl group at C-5 attacks the $\text{CH=O}$ group from bottom side. The mechanism for the cyclization of $\text{D-allose}$ to its $\text{β-D-allopyranose}$ form is

Conclusion

The Haworth projection of $\text{β-D-allopyranose}$ is drawn with six membered ring, indicating appropriate stereochemistry and placing the hydroxyl group up at anomeric carbon.

Interpretation Introduction

(c)

Interpretation:

The Haworth projection for given molecule is to be drawn.

Concept introduction:

Structural drawings of carbohydrates in cyclic forms are called Haworth formulas. The $\text{CH=O}$ functional group is converted to a hemiacetal where the carbonyl carbon becomes a new asymmetric carbon called anomeric carbon. Two types of cyclic forms can be drawn – one is pyranose, having six membered ring with one oxygen, and furanose, having five membered ring with one oxygen. For the pyranose, the hydroxyl group at C-5 forms a bond with $\text{CH=O}$ group, and for furanose, the hydroxyl group at C-4 forms a bond with $\text{CH=O}$ group. In a Fischer projection, the substituents to the right are down, and those to the left are up in the corresponding Haworth formula. For the $\text{D}$ series of carbohydrates, if the hydroxyl group at anomeric carbon is down, the configuration at that carbon is $\text{α}$, and if the hydroxyl group is up, the configuration at anomeric carbon is $\text{β}$.

Answer to Problem 18.73P

The Haworth projection of $\text{α-D-allofuranose}$ is

Explanation of Solution

The given molecule is $\text{α-D-allofuranose}$.

The structure of $\text{α-D-allofuranose}$ can be drawn from the Fischer projection of $\text{D-allose}$. The Fischer projection of $\text{D-allose}$ is

The name $\text{α-D-allofuranose}$ suggests that the ring must be five membered, where the the hydroxyl group at anomeric carbon must be down. Thus, the hydroxyl group at C-4 attacks the $\text{CH=O}$ group from up side. The mechanism for the cyclization of $\text{D-allose}$ to its $\text{α-D-allofuranose}$ form is

Conclusion

The Haworth projection of $\text{β-D-allopyranose}$ is drawn with five membered ring indicating appropriate stereochemistry and placing the hydroxyl group down at anomeric carbon.

Interpretation Introduction

(d)

Interpretation:

The Haworth projection for given molecule is to be drawn.

Concept introduction:

Structural drawings of carbohydrates in cyclic forms are called Haworth formulas. The $\text{CH=O}$ functional group is converted to a hemiacetal where the carbonyl carbon becomes a new asymmetric carbon called anomeric carbon. Two types of cyclic forms can be drawn – one is pyranose, having six membered ring with one oxygen, and furanose, having five membered ring with one oxygen. For the pyranose, the hydroxyl group at C-5 forms a bond with $\text{CH=O}$ group, and for furanose, the hydroxyl group at C-4 forms a bond with $\text{CH=O}$ group. In a Fischer projection, the substituents to the right are down, and those to the left are up in the corresponding Haworth formula. For the $\text{D}$ series of carbohydrates, if the hydroxyl group at anomeric carbon is down, the configuration at that carbon is $\text{α}$, and if the hydroxyl group is up, the configuration at anomeric carbon is $\text{β}$.

Answer to Problem 18.73P

The Haworth projection of $\text{β-D-allofuranose}$ is

Explanation of Solution

The given molecule is $\text{β-D-allofuranose}$.

The structure of $\text{β-D-allofuranose}$ can be drawn from the Fischer projection of $\text{D-allose}$. The Fischer projection of $\text{D-allose}$ is

The name $\text{β-D-allofuranose}$ suggests that the ring must be five membered, where the the hydroxyl group at anomeric carbon must be up. Thus, the hydroxyl group at C-4 attacks the $\text{CH=O}$ group from down side. The mechanism for the cyclization of $\text{D-allose}$ to its $\text{β-D-allofuranose}$ form is

Conclusion

The Haworth projection of $\text{β-D-allopyranose}$ is drawn with five membered ring indicating appropriate stereochemistry and placing the hydroxyl group up at anomeric carbon.