https://doi.org/10.1351/goldbook.S05976
A prefix to specify @C01249@ (absolute or relative) or @C01258@. For example @R05423@; @R05424@; @H02763@; @R05308@; @E01882@; @A00410@; etc.
Source:
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2218 [Terms] [Paper]