Chapter 5, Problem 5.65P

Interpretation Introduction

Interpretation:

The aldopentoses that are related as $\text{C2}$ epimers and $\text{C3}$ epimers are to be identified.

Concept introduction:

$\text{D-aldopentoses }$ have three $\text{H - C - OH}$ groups are added into the glyceraldehyde, which has three stereochemical configurations. Thus, $\text{D-aldopentoses }$ have four possible structures, $\text{D-ribose, D-arabinose, D-xylose, and D-lyxose}$. In the Fisher projection of $\text{D-aldopentoses }$, $\text{C1}$ is an aldehyde carbon, and the $\text{OH}$ group added to the asymmetric carbon appears on the right side and shown in blue color. The Fisher projections of $\text{D-aldopentoses }$ are shown below:

Diastereomers are stereoisomers that contain two to more chiral centers, and that are not mirror images of each other.

Epimers are the optical isomers that contain two or more chiral centers but differ from each other in the configuration of a single carbon atom.