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. Naming Sugars in the (R,S) System Use the inform tit ion in the Critical Developments in Biochemistry box titled "Rules for Description (if Chiral Centers in the ( R.S ) System" (Chapter 4) to name D-galactose using ( R.S ) nomenclature. Do the same for L-altrone.

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Textbook Question

Chapter 7, Problem 7P

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.

Naming Sugars in the (R,S) System Use the inform tit ion in the Critical Developments in Biochemistry box titled "Rules for Description (if Chiral Centers in the (R.S) System" (Chapter 4) to name D-galactose using (R.S) nomenclature. Do the same for L-altrone.

Expert Solution & Answer

Interpretation Introduction

Interpretation:

The name ofD−galactoseandL−altroseby using(R,S)nomenclature are to be stated.

Concept introduction:

A carbon atom that has four non-equivalent atoms or groups attached to it is known as chiral carbon atom. Chiral carbon centers are also called as asymmetric or stereogenic centers.

The naming of chiral center and geometric isomers are based on Cahn-Ingold-Prelog priority rules. If the priority assigned to each group attached to the chirality center in a molecule is in a clockwise direction, then it is the R-stereoisomer, and if this is counter-clockwise, then it is the S-stereoisomer. R and S-stereoisomer are mirror images of each other.

Answer to Problem 7P

The name ofD−galactoseandL−altroseby using(R,S)nomenclature are2R, 3S, 4S, 5R−D−galactoseand2R, 3S, 4S, 5S−L−altroserespectively.

Explanation of Solution

The highest priority group in case of a monosaccharide is hydroxyl(OH)group. Thus, the lowest numbering will be given to the hydroxyl(OH)group.

The Fischer projection structure forD−galactoseis shown below.

Biochemistry, Chapter 7, Problem 7P , additional homework tip 1

Figure 1

The substituents which extend to the side ofD−galactoseare supposed to be bent on the side of viewer. All the other carbon atoms in the Fischer structure is bend away from the viewer.

Thus, in the structure ofD−galactose, the substituents are arranged around each carbon atoms. AtC−2position, the priority order of the substituents isOH>CHO>C−3>H. After the rotation of bend structure ofD−galactosemolecule, hydrogen atom behindC−2position flips the hydroxyl group at the left position and the aldehyde group at the upper right position. Thus, the priority of the groups is in a clockwise direction. Hence,C−2position is assigned asR-configuration.

AtC−3position, the priority order of the substituents isOH>C−2>C−4>H. The carbon atC−2has higher priority due to the presence of an aldehyde group on it. After the rotation of bend structure, hydrogen atom behindC−3position flips the hydroxyl group at the right position andC−2at the upper left position. Thus, the priority of the groups is in an anti-clockwise direction. Hence,C−3position is assigned asS-configuration.

AtC−4position, the priority order of the substituents isOH>C−3>C−5>H. The carbon atC−3has higher priority due to the bonding ofC−5with two hydrogen atoms. After the rotation of bend structure, hydrogen atom behindC−4position flips the hydroxyl group at the right position andC−3at the upper left position. Thus, the priority of the groups is in an anti-clockwise direction. Hence,C−4position is assigned asS-configuration.

AtC−5position, the priority order of the substituents isOH>C−4>C−6>H. The carbon atC−4has higher priority due to its bonding with other carbon. After the rotation of bend structure ofD−galactosemolecule, hydrogen atom behindC−5position flips the hydroxyl group at the left position andC−4at the upper right position. Thus, the priority of the groups is in a clockwise direction. Hence,C−5position is assigned asR-configuration.

Thus, the name ofD−galactosethat can be assigned by using(R,S)nomenclature is2R, 3S, 4S, 5R−D−galactose.

The Fischer projection structure forL−altroseis shown below.

Biochemistry, Chapter 7, Problem 7P , additional homework tip 2

Figure 2

The substituents which extend to the side ofL−altroseare supposed to be bent on the side of viewer. All the other carbon atoms in the Fischer structure is bend away from the viewer.

Thus, in the structure ofL−altrose, the substituents are arranged around each carbon atoms. AtC−2position, the priority order of the substituents isOH>CHO>C−3>H. After the rotation of bend structure ofL−altrosemolecule, hydrogen atom behindC−2position flips the hydroxyl group at the left position and the aldehyde group at the upper right position. Thus, the priority of the groups is in a clockwise direction. Hence,C−2position is assigned asR-configuration.

AtC−3position, the priority order of the substituents isOH>C−2>C−4>H. The carbon atC−2has higher priority due to the presence of an aldehyde group on it. After the rotation of bend structure, hydrogen atom behindC−3position flips the hydroxyl group at the right position andC−2at the upper left position. Thus, the priority of the groups is in an anti-clockwise direction. Hence,C−3position is assigned asS-configuration.

AtC−4position, the priority order of the substituents isOH>C−3>C−5>H. The carbon atC−3has higher priority due to the bonding ofC−5with two hydrogen atoms. After the rotation of bend structure, hydrogen atom behindC−4position flips the hydroxyl group at the right position andC−3at the upper left position. Thus, the priority of the groups is in an anti-clockwise direction. Hence,C−4position is assigned asS-configuration.

AtC−5position, the priority order of the substituents isOH>C−4>C−6>H. The carbon atC−4has higher priority due to its bonding with other carbon. After the rotation of bend structure ofL−altrosemolecule, hydrogen atom behindC−5position flips the hydroxyl group at the right position andC−4at the upper left position. Thus, the priority of the groups is in an anti-clockwise direction. Hence,C−5position is assigned asS-configuration.

Thus, the name ofL−altrosethat can be assigned by using(R,S)nomenclature is2R, 3S, 4S, 5S−L−altrose.

Conclusion

The name ofD−galactoseandL−altroseby using(R,S)nomenclature are2R, 3S, 4S, 5R−D−galactoseand2R, 3S, 4S, 5S−L−altroserespectively.

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