Glyceraldehyde has a chiral center and therefore exists as two different enantiomers with opposite optical rotation:
| Name of enantiomer | D-glyceraldehyde (R)-glyceraldehyde (+)-glyceraldehyde | L-glyceraldehyde (S)-glyceraldehyde (−)-glyceraldehyde |
| Fischer projection | ||
| Skeletal formula | ||
| Ball-and-stick model |
While the optical rotation of glyceraldehyde is (+) for R and (−) for S, this is not true for all monosaccharides. The stereochemical rotation can only be determined by the chemical structure, whereas the optical rotation can only be determined empirically (by experiment).
Glyceraldehyde is used as the configurational standard for carbohydrates. Monosaccharides with an identical conformation at the last stereocentre, for example, C5 for glucose, to (R)-glyceraldehyde are assigned the stereo-descriptor D, those similar to (S)-glyceraldehyde are assigned a L. Both, D and L, should be small capital letters.
Glyceraldehyde can be prepared, along with dihydroxyacetone, by the mild oxidation of glycerol, for example with hydrogen peroxide and a ferrous salt as catalyst.
It was by a lucky guess that the D molecular geometry was assigned to (+)-glyceraldehyde in the late 19th century, as confirmed by x-ray crystallography in 1951.