The letters ‘D’ or ‘L’ before the name of any compound indicate the
relative configuration of a particular stereoisomer of a compound with
respect to configuration of some other compound, configuration of
which is known In the case of carbohydrates, this refers to their
relation with a particular isomer of glyceraldehyde Glyceraldehyde
contains one asymmetric carbon atom and exists in two enantiomeric
forms as shown below (+) Isomer of glyceraldehyde has ‘D’ configuration