https://doi.org/10.1351/goldbook.F02392
An arbitrary convention according to which (+)-glyceraldehyde, now known to be (R)-2,3-dihydroxypropanal, was named d-glyceraldehyde (with the @[email protected] l-glyceraldehyde and its @[email protected] dl-glyceraldehyde) and taken to have the @[email protected] represented by the @[email protected] formula shown in the diagram.
F02392.png
The atom numbered 1 according to normal nomenclature rules is conventionally placed at the top of the main chain, which is drawn vertically and other groups are drawn on either side of that main chain. The convention is still in use for α-amino acids and for @[email protected]
Source:
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2208 [Terms] [Paper]