Absolute configuration of glyceraldehyde

Absolute configurations of the amino acids are referenced to D- and L-glyceraldehyde on the basis of chemical transformations that can convert the molecule of interest to either of these reference isomeric structures. In such reactions, the stereochemical consequences for the asymmetric centers must be understood for each reaction step. Propose a sequence of reactions that would demonstrate that l( —)-serine is stereochemically related to l( —)-glyceraldehyde. 

Glycal assembly method, 1002 (4- )-Glyceraldehyde. absolute configuration of, 980 (-)-Glyceraldehyde, configuration of, 300... 

Fischer s Convention. Initially, the absolute configurations of optical isomers were unknown to chemists working with optically active compounds. Emil Fischer, the father of carbohydrate chemistry, decided to relate the possible configurations of compounds to that of glyceraldehyde of which the absolute configuration was yet unknown but was defined arbitrarily. 

At the time the choice of absolute configuration for glyceraldehyde was made, there was no way of knowing whether the configuration of (-l-)-glycer-aldehyde was in reality 3a or 3b. However, the choice had a 50% chance of... 

We now know the absolute configurations of (+) - and (—) -glyceraldehyde. These structures serve as the configurational standards for all monosaccharides. 

At the time the d and l system of relative configurations was introduced, chemists could not determine the absolute configurations of chiral compounds. They decided to draw the d series with the glyceraldehyde OH group on the right, and the l series with it on the left. This guess later proved to be correct, so it was not necessary to revise all the old structures. 

Figure 11.2. d-Aldoses containing three, four, five, and six carbon atoms, d-Aldoses contain an aldehyde group (shown in blue) and have the absolute configuration of d-glyceraldehyde at the asymmetric center (shown in red) farthest from the aldehyde group. The numbers indicate the standard designations for each carbon atom. 

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