The simplest carbohydrates glyceraldehyde is chosen as the standard, to assign D and L configuration to monosaccharides.
Glyceraldehyde contains one asymmetric carbon atom and exist in two enantiomeric forms
The dextro entantiomer is represented as (+) glyceraldehyde and it is referred as D-configuration i.e., D-glyceraldehyde.
The laevo enantiomer of glyceraldehyde is represented as (-) glyceraldehyde and it corelated as Lconfiguration i.e., L-glyceraldehyde.
In Fischer projection formula,
A monosaccharide is assigned D-configuration if the (- OH) hydroxyl group at the last chiral carbon and lies towards right hand side.
On the other hand it is assigned L-configuration if the – OH group on the last chiral carbon atom and lies on the left hand side.
In monosaccharides, the most oxidised carbon (i.e., -CHO) is at the top.
Examples :
