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D‐, L‐, and DL‐ Prefixes to chemical names for compounds that have a centre of asymmetry in the molecule, and which can therefore have two forms (isomers).

Most naturally occurring sugars have the d‐conformation; apart from a few microbial proteins and some invertebrate peptides, all the naturally occurring amino acids have the l‐configuration. Chemical synthesis yields a mixture of the d‐ and l‐isomers (the racemic mixture), generally shown as dl‐. See also R‐.