Chapter 19, Problem 21P

(a)

Interpretation Introduction

Interpretation: The full name along with the anomeric designation of the following compound should be determined:

Concept Introduction: A common way of writing structural formula which represent the cyclic structure of monosaccharides is said to be the Haworth projection, which is best represented by chair conformations.

A convention used to represent a 3-D stereo formula in 2-D representation is said to be Fischer projections. In this projection, the vertical lines represent bonds below the plane of the paper and horizontal lines represents bonds above the plane of the paper.

Answer to Problem 21P

$\text{α-D-}$ Galactose.

Explanation of Solution

Drawing the Fischer projection of given compound as:

For a D-sugar, the group attached to the bottom chiral carbon is present at the right-hand side whereas for L-sugar it is present at left-hand side.

A new carbon stereocenter created by the conversion of an open structure to a cyclic structure is said to be the anomeric carbon. In carbohydrates, when the hydroxy group on an anomeric carbon is present on the same side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, then it is designated as beta, $\beta$ whereas when the hydroxy group on an anomeric carbon is present on the opposite side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, then it is designated as alpha, $\alpha$ .

The anomeric carbon of the given compound is shown by “*”:

Since, in the given sugar the $\text{-OH}$ group in $\text{C-5}$ position is at right-hand side so, the sugar is D-sugar. And the hydroxy group on an anomericis present on the opposite side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, so it is designated as alpha, $\alpha$ .

Hence, the name of compound is $\text{α-D-}$ Galactose.

(b)

Interpretation Introduction

Interpretation: The full name along with the anomeric designation of the following compound should be determined:

Concept Introduction: A common way of writing structural formula which represent the cyclic structure of monosaccharides is said to be the Haworth projection, which is best represented by chair conformations.

A convention used to represent a 3-D stereo formula in 2-D representation is said to be Fischer projections. In this projection, the vertical lines represent bonds below the plane of the paper and horizontal lines represents bonds above the plane of the paper.

Answer to Problem 21P

$\text{α-D-}$ Fructose.

Explanation of Solution

Drawing the Fischer projection of given compound as:

For a D-sugar, the $\text{-OH}$ group attached to the bottom chiral carbon is present at the right-hand side whereas for L-sugar it is present at left-hand side.

A new carbon stereocenter created by the conversion of an open structure to a cyclic structure is said to be the anomeric carbon. In carbohydrates, when the hydroxy group on an anomeric carbon is present on the same side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, then it is designated as beta, $\beta$ whereas when the hydroxy group on an anomeric carbon is present on the opposite side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, then it is designated as alpha, $\alpha$ .

The anomeric carbon of the given compound is shown by “*”:

Since, in the given sugar the $\text{-OH}$ group in $\text{C-5}$ position is at right-hand side so, the sugar is D-sugar. And the hydroxy group on an anomeric is present on the opposite side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, so it is designated as alpha, $\alpha$ .

Hence, the name of compound is $\text{α-D-}$ Fructose.

(c)

Interpretation Introduction

Interpretation: The full name along with the anomeric designation of the following compound should be determined:

Concept Introduction: A common way of writing structural formula which represent the cyclic structure of monosaccharides is said to be the Haworth projection, which is best represented by chair conformations.

A convention used to represent a 3-D stereo formula in 2-D representation is said to be Fischer projections. In this projection, the vertical lines represent bonds below the plane of the paper and horizontal lines represents bonds above the plane of the paper.

Answer to Problem 21P

$\text{α-D-}$ Glucose.

Explanation of Solution

Drawing the Fischer projection of given compound as:

For a D-sugar, the $\text{-OH}$ group attached to the bottom chiral carbon is present at the right-hand side whereas for L-sugar it is present at left-hand side.

A new carbon stereocenter created by the conversion of an open structure to a cyclic structure is said to be the anomeric carbon. In carbohydrates, when the hydroxy group on an anomeric carbon is present on the same side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, then it is designated as beta, $\beta$ whereas when the hydroxy group on an anomeric carbon is present on the opposite side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, then it is designated as alpha, $\alpha$ .

The anomeric carbon of the given compound is shown by “*”:

Since, in the given sugar the $\text{-OH}$ group in $\text{C-5}$ position is at right-hand side so, the sugar is D-sugar. And the hydroxy group on an anomeric is present on the opposite side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, so it is designated as alpha, $\alpha$ .

Hence, the name of compound is $\text{α-D-}$ Glucose.

(d)

Interpretation Introduction

Interpretation: The full name along with the anomeric designation of the following compound should be determined:

Concept Introduction: A common way of writing structural formula which represent the cyclic structure of monosaccharides is said to be the Haworth projection, which is best represented by chair conformations.

A convention used to represent a 3-D stereo formula in 2-D representation is said to be Fischer projections. In this projection, the vertical lines represent bonds below the plane of the paper and horizontal lines represents bonds above the plane of the paper.

Answer to Problem 21P

$\text{β-D-}$ Mannose.

Explanation of Solution

Drawing the Fischer projection of given compound as:

For a D-sugar, the $\text{-OH}$ group attached to the bottom chiral carbon is present at the right-hand side whereas for L-sugar it is present at left-hand side.

A new carbon stereocenter created by the conversion of an open structure to a cyclic structure is said to be the anomeric carbon. In carbohydrates, when the hydroxy group on an anomeric carbon is present on the same side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, then it is designated as beta, $\beta$ whereas when the hydroxy group on an anomeric carbon is present on the opposite side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, then it is designated as alpha, $\alpha$ .

The anomeric carbon of the given compound is shown by “*”:

Since, in the given sugar the $\text{-OH}$ group in $\text{C-5}$ position is at right-hand side so, the sugar is D-sugar. And the hydroxy group on an anomeric is present on the same side as that of the ${\text{-CH}}_{\text{2}}\text{OH}$ group, so it is designated as beta, $\text{β}$ .

Hence, the name of compound is $\text{β-D-}$ Mannose.