While the optical rotation of glyceraldehyde is (+) for R and (−) for S, this is not true for all monosaccharides. The stereochemical configuration can only be determined from the chemical structure, whereas the optical rotation can only be determined empirically (by experiment).
It was by a lucky guess that the molecular D- geometry was assigned to (+)-glyceraldehyde in the late 19th century, as confirmed by X-ray crystallography in 1951.[2]
Nomenclature
In the D/L system, glyceraldehyde is used as the configurational standard for carbohydrates.[3] Monosaccharides with an absolute configuration identical to (R)-glyceraldehyde at the last stereocentre, for example C5 in glucose, are assigned the stereo-descriptor D-. Those similar to (S)-glyceraldehyde are assigned an L-.
^Determination of the Absolute Configuration of Optically Active Compounds by Means of X-Rays Nature 168, 271-272 J. M. BIJVOET, A. F. PEERDEMAN & A. J. van BOMMEL doi:10.1038/168271a0