Draw and name the enantiomers of the sugars shown in Figure 23-2. Give the relative configuration (D or L) and the sign of the rotation in each case.

Molecules having exact mirror images of itself and has non- super imposable mirror image is known as a chiral molecule. Enantiomers or optical isomers are two mirror images of a chiral molecule.

If a compound rotates plane polarised light to the right, then it is said to be dextrorotatory $\left(\mathrm{D}\right)$. This is indicated in the name of the compound by the prefix sign $\left(+\right)$. But if a compound rotates plane polarised light to the left, then it is said to be laevorotatory $\left(\mathrm{L}\right)$. This is indicated in the name of the compound by the prefix sign That is, it can be said that $\mathrm{D}‐\mathrm{and}\mathrm{L}‐$ refers to the absolute configuration around the asymmetric carbon atom while (+) and (-) refers to the direction of rotation of the plane polarised light.

For D-series, OH group of the bottom asymmetric carbon is present on the right side in the Fischer projection while for L-series, OH group of the bottom asymmetric carbon is present on the left side in the Fischer projection.

Glucose is an aldohexose. For glucose, the enantiomers are D(+)glucose and L(+)glucose. The structure of both the enantiomers are shown below.

Arabinose is an aldopentose. For arabinose, the enantiomers are D(-) arabinose and L(-)arabinose. The structure of both the enantiomers are shown below.

Erythrose is an aldotetrose. For erythrose, the enantiomers are D(-)erythrose and L(-)erythrose. The structure of both the enantiomers are shown below.

Glyceraldehyde is an aldotriose. For glyceraldehyde, the enantiomers are D(+)glyceraldehyde and L(-)glyceraldehyde. The structure of both the enantiomers are shown below.